Prolog replace element in list. Inside this list, I have three inner lists.
Prolog replace element in list The reasoning behind this is explained by how _ works: it names an anonymous variable, and each instance of _ names a different variable. How can I replace an element of a list using an index in PROLOG. If you would like to apply it to the non-ground case, you first need to make the terms ground (freeze), then call remove/3, and finally return to the non-ground case (melt_new). But using (is)/2 won't work because it only operates on numbers. memberchk/2 is similar So I have a program that has a predicate to replace the first occurrence of some element of a list with a given new element and produce a new list. You can play that out as follows. match([Elem|Tail],Num,Num,Elem). I’d like to have a Prolog predicate that can replace the nth item in the list with the first. Program in Prolog that returns change. length_slower_than_builtin(Lst, 1) (Once = true -> ! ; true). Replacing a variable in prolog. Once you checked that the item is nonnegative you know that the item will be on the resulting list. Transpose matrix in prolog. 6. We give repl the term we'd like to replace and the term we'd like to replace it with, and if A happens to be that term in the list, we replace it with B, otherwise we keep it. A difference list can be used to “append” in the intended order. Predicate remove as defined above will work as you expect only for lists of (lists of) ground terms (= terms with no variables). Replace a tree node in a matched location of a binary tree. The problem is with the last case. Should you pass a variable into Element, you could use this function to list all of the elements of the List you pass in, like the writelist function above, but it is recommended you use writelist or some other function for that behavior. Return vowels from word. I can see where you're headed with your solution, but you needn't bother with so much arithmetic in this case. Prolog: update element of list. Think about what your Count the number of element in the list before call the predicate that delete the last element. Errors - List is type-checked. Method that counts the number of occurs in one list in Prolog. Next, Prolog tries to unify Y with [], again trivially succeeding, but this time establishing the binding Y = [] which it reported to you. L = [1, 2, 1, 4, 5] Z = 1 This code replaces the nth item in the list with the last. It can easily be define by retrieving, the 3. The base case and the case where the item is negative are right. Example: L = [1,2 Prolog: replace an element in a list at a specified index. Prolog - Search a list for an element, print the list if element is found. For example: I have a list of list and a list. In Prolog, [X|T] is the list that starts with X Obtaining the first elements. Option 1 here would be the Obtaining the first elements. Step 1 is done with setof(X, member(X, Y), L) and it works in two ways. Some examples: An empty list: [] is represented as the atom it is: [] A list of one element, [a] is internally stored as. how to check if B isn't betwenn A and B. Hot Network Questions Fast allocation-free alphanumeric comparer used for sorting "Devastate" in "Wuthering Heights" How make leftbar like this? Replace the Engine, rebuild, or just put on new rings But just as an exercise I decided to try and create a predicate that could append an element to the end of a list, without using append. Note that empty lists are removed. Hot Network Questions In Prolog, functions work by recursion rather than iteration. Replacing elements in list of lists PROLOG. How do I check if a list is empty? 4448. Variable in Prolog. element of the matrix-list. asked Mar 13, 2016 at 12:15. The second part invokes dosomething rule recursively on the tail of the list. ?- L=[a,b,c,d To find the nth element of a list (where n is relative to zero), something like this ought to suffice: find_nth_element_of_list( 0 , X , [X|_] ) . Trying to replace second or It's slower: using a list of 10 million elements, and replacing the last one, then your second version takes 2. For example: my list is [1,2,3,4,5] and I want to insert 0 after every element. Before the next step, you have to get a notational change. We should start with an access predicate: nth0(?Index, ?List, ?Element) nth1(?Index, ?List, ?Element) and generalise it in a replaceall(Item,Repl,[H|T],[Repl|List]) :-H = Item, !, replaceall(Item,Repl,T,List). 0 and True when Set has the same elements as List in the same order. If we reverse this list, we'll end up with the "middle" list in the correct order and First slapped on the end (this list is called B) so we've got the original first element as the last element of this list and all the right middle elements. Hot Network Questions If you are working remotely as a contractor, can you be allowed to applying as a business vistor to Australia? How can quantum mechanics so It works when I replace term with an empty String or some random String. The solution by @WillemVanOnsem, derived from the OP code, uses term unification when comparing the element to be removed with the elements of the list (an alternative would be to use term equality). If I want to swap ONLY the first two elements, I would write, [Y, X|T] so I have swapped X and Y , but keep the same tail, T (I do not want to swap any more elements). So the resulting list should be: [1,0,2,0,3,0,4,0,5,0]. find_nth_element_of_list( N , X , [_|Xs] ) :- N > 0 , N1 is N-1 , find_nth_element_of_list( N1 , X , Xs ) . An example is then: PROLOG store nth element of list if string is found in list. Delete vowels in a list. 2. List elements list, prolog-usage. Using the build-in predicate member/2, the differs/2 will look like this: I would like to find a method to find the most repeated element in a list if two elements repeat the same number of times. element_at(X,[X|_],1). I want to update the list of list by using the element from the second list. When the tail list is empty, the first clause would unify, thus ending the This is also the stop condition. I You may be unsure about the fact that the list you want to replace contains elements starting with uppercase letters, i. Then for each X from the list built on 1) discard this element from the input list to get the output list Z without member X. You'd skip the PROLOG store nth element of list if string is found in list. Provide details and share your research! But avoid . However, the element X is the last and only element in the list [X]. One is to use a key-value pair with the hyphen functor. This says "empty lists are unique. I am trying to write two predicates. 5. Do anyone have an idea how can to make this? EDIT: The internal lists contain 1-5 elements. This is also the stop condition. Replacing atom with corresponding value from a list in Prolog. modify([],X,[(X,1 I want to write a predicate that will insert a given element after every element in a list and will print resulting list. For list processing, this means (in general) you have to decide how to handle the empty list and how to handle an element in front of some other list. How do I make a flat list out of a list of lists? 3222. Should we use "by" to replace "from" in "a support piling knocked off about a year ago from the powerful king tides"?. Prolog: last element and the rest of a list. Example: % replace(+List,+Counter,-New List, %-First Item). Initially, the variable is n, then on some occasions I would like to change it to a. list; prolog; element; or ask your own question. In that case we first calculate the length of H, we the calculate (through recursion) the Here we only can query in one direction: if we unify a list of 2-tuples with the second argument, then Prolog can not derive the elements in the first list. As with (nearly) all predicates with list processing, you can split your predicate in two types of clauses: base clauses: in many cases these lists deal with empty lists. To replace every other item, you can do it a couple of ways: Pull items off 2 at a time. Count specific element in list [Prolog] 1. In standard Prolog, this implies that the atom '[]' is removed too. I am very new to Prolog and I am having some difficulties understanding the backtracking and recursion. Which is easy to do - just use the built-in library function zip, as follows: for a_element, m_element in zip(a, m): s[a_element] = m_element To make it work the way you were trying to do it, you would have to get a list of indices to iterate Sum only the positive elements in a list in prolog. removeAll(X, [X|T], L Prolog: replace an element in a list at a specified index. I have made use of this and recuresed overs You can do it recursively: Suppose 0-based index (otherwise just change the 0 with 1 on the first clause) indexOf([Element|_], Element, 0). Whether the speed difference matters will depend on how often you need to do such a Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. This is actually easier that try to verify that every element of A is present in B. How can I replace a list in Prolog? Hot Network Questions Contradiction I have to write the tr rule to translate all occurrences of a list element value to another value. Share. an empty list [], in which case the total number is of course zero; and; a non-empty list [H|T], where H is a list, and T is the list of remaining lists. How do I clone a list so that it doesn't change unexpectedly after assignment? 2325. I`d like to have a procedure for replacing elements in matrix like: , Levels1 = [Nth0Prev|LevelsT], % Iterate through the list to the desired element replace_matrix_(T, Levels1, NewVal, NewMatrix1) ; LevelsT = [] % Replace this element, because am at the lowest level -> NewMatrix = [NewVal I’d like to have a Prolog predicate that can replace the nth item in the list with the first. I am new to Prolog. Prolog: replacing an element in a list with another list. How to eliminate from a list [b,a] if already exist [a,b] Hot Network Questions Bitcoin Core Development I think you must prove the following: move(L, X, From, To, R) is the predicate you want run, so the #1 argument is a list of list (in the sample: L = [[a,b,c], [d,e,f],[h,g]]); the #3 and #4 arguments are members of L, so you can use the predicate nth1(N, L, E), where N is the order of the element, L is the list and E the Element; each element Prolog: replace an element in a list at a specified index. The list can have repeated elements. It works, but my question is can this rule be written otherwise: elemen I can search for a element inside a list, if the element is found in the list, then the list is printed out to confirm that it has been found. I. Let's call Your definition of changeFst/4 is incorrect on many counts like changeFst(o,[o,o],n,[m,y,s,t,e,r,y]). @lurker: au contraire. See also sort/2 can be used to create an ordered set. Finally, prolog is more efficiente if the rules are tail recursive (if the execution environment is Basically you want to implement a set; check the list manual page for set operations. (a,[]) Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company Visit the blog You can start by building a predicate differs/2 that verify if any of the elements on the list A is not member of the list B. The solution works for ground terms. Hot Network Questions Variable SQL join operator using case statement Prolog element in lists replacement. 2)If you have input [H,Y|T] (a list with at least two elements H,Y and a tail of the list) and H\=Y you call remove_duplicates2([Y|T],T1) and you have stored H to the List you want to return. Any ideawhy? I use swi prolog, you could use a replace predicate (found in other stack overflow questions), combined with a flatten operator on a list: Prolog - Search a list for an element, print the list if element is found. How to remove an element from a list by index. Replace every instance of a list by another ONE by ONE in Prolog. 1. Ouput is List, which is a variable, hence changing is not possible. Therefore you should do the recursion and return a list that contains the element you have checked (H) and the list returned by recursion. Obtaining the first elements. PROLOG - Change elements in a list. Inside this list, I have three inner lists. List elements replace with other elements in prolog. 5432. The method replace receives the row number and the column (position) number and the new value for the position. In Prolog "an element which appears only one time in a list" can be translate by. Replace particular leaves in a tree, without destroying structure of tree. Pairs is a list of Item-Count pairs that represents the run length encoding of Items Removing Duplicate Elements from List of Lists in Prolog. How do I do it? Skip to main content. prolog how to remove an element from a list? 0. 1 seconds, and his version with a cut in the first clause and the I > 0 test removed from the second takes 1. Replacing in this list the 2 element and than replacing the 3 element. Prolog List Squaring, Modifying element in List. replace(E,S,[H|T1],[H|T2]):-E\=H, replace(E,S,T1,T2). Prolog recursively replace elements of list with elements of another list. Several systems provide a flatten/2 library predicate over lists that may be useful, however, if you cannot avoid this representation. The last query corresponds to the question: What must A and B look like such that a two element list will remain the same? There are four answers: A, B, X, and Y are all the same. Another way of saying it is: to append a non-empty list A to another list B, first append the tail of A to B and then add the head of A to the front of the list. 4. How to get n-th element of a list when a list starts from 1 (index) ? How can I transform this, which gets n-th element, but list starts from 0 index. It's because you used these variables ones but note elsewhere. I think you need to define the first clause of replaceX with: replaceX(A,_,0,_,A):-!. The reason is your incorrect usage of cuts. Clause #1 says, X is the second to last element in list [X]. inductive clauses: in this case both lists are not empty. [[a,b,c], [d,e,f],[h,g]] I need to write a predicate called "move(L, X, From, To, R)" where X is the character I want to move (this character has to be the last element in the inner list), From is the index of list I want to move from, To is the index of list I want to move to. Add to list if not already in list, change elements in list (PROLOG) 1. Prolog: How to find a specific element in a list? 3. There are a couple of ways to include a "key value". Note that that this predicate uses a slightly different representation for key-value pairs expressing A list that has at least two elements looks like [X, Y|T] (the first two elements are X and Y - variables). Ys = [a-3, b-2, d-1, c-1]. Assuming that the list of lists in your example have been flatted, you should be able to write a simple recursive predicate to walk over the list and process each element that However, if the list is 3 or more elements, it seems clear that X will become irrelevant (as will be seen in clauses 2 and 3). If you can find an element on A that fulfill this condition, then you can affirm that A is not contained in B. Surely this is far better (although not as fast as the builtin length/2: length_slower_than_builtin(Lst, Len) :- (nonvar(Len) -> Once = true ; Once = false), length_slower_than_builtin_(Lst, 0, Len), % To prevent infinite loop with e. Modified 9 years, 8 months ago. Elements E1 and E2 are considered duplicates iff E1 == E2 holds. List elements In order for this function to succeed as intended, you must pass a value into Element, and a list into List. Follow how to compare elements of a lists in prolog. Asking for help, clarification, or responding to other answers. We will first display and show This function is used to replace an element in a list. e. Transposing a Matrix in prolog. Prolog element in lists replacement. " This is a helpful property. How to say if an element belongs to a list in Prolog? 1. Skip to main content. replacing elements between two lists using prolog. They are to replace the second or second last element of a list with a given input element. A simple version might be designed like this: (define (replace old-element new-element list) ; if the list is null, just return null ; else if the car of the list is equal to old-element ; run replace on the rest of the list, and cons new-element onto it ; else ; run replace on the rest of the list, and cons the car onto it) I am new to Prolog, and I want to change the value of a variable, which is extracted from a list. Go with the first if the candidates are facts. To go past that, you might use read_line_to_string(user_input, Text) instead of read(X) and split_string/4 to split on spaces and turn it into words, and then change your facts to use strings instead of atoms or pay atention to converting between strings and atoms, and then apply change to them, and then use atomics_to_string/3 to build the response string before I am new to Prolog, and I want to change the value of a variable, which is extracted from a list. Steven Steven. Prolog replace each instance of a constant in a list with a variable. g. It takes in four arguments. Find the unique elements only that are not in both two lists. Similarly, to remove the nth element of a list, something like this ought to suffice: Replace elements of a list in Prolog. It could be easy with the approach: I change the expression to list using T=. 0 seconds. edit Yet another way, the better from the efficiency viewpoint, make use of non-backtrackable assignment. Prolog: Matrix operations. Viewed 2k times 1 . 3. Say I have a list of facts say 6 facts the first column of numbers represents the persons ID, and then select the element - O(N log N) in time. How do you do a search and replace of a list with another sublist in Prolog? 1. Prolog replace element in a list with another list. unique([]). How do you calculate the total number of elements in a list when there can be lists within a list? use maplist to replace each list by it's length, then sum up the lengths. Using a Prolog rule to display the first element of a given list, within a query? 0. Filtering elements from a list based on conditions in prolog. The complexity of the implementation is N*log(N). false. I would like to move elements in a list in prolog to a new location within the same list, similar to a cut & paste operation. succeeds, but clearly it should fail. Try this to replace the even number list elements (where the 1st element in the list is item number 1. You need to use the [A|_] pattern: indeed a list where the head is A, and we are not interested in the rest (tail). [A, _] unifies with a list that contains exactly two elements, but this will thus fail for lists with more than two elements, or with one elements, like you found out. I have it done like so: I just started prolog and am trying to understand lists. In standard Prolog, Pairs is a list of Item-Count pairs that represents the run length encoding of Items. i should write a rule on prolog, which finds the last element of a list and add 1 to it. The things is I have . So far I have only been able to replace the first element of a list or insert at position two. Note that you dont have to convert a list to a set (a list is a set as long as it doesnt have duplicates; The solution by @WillemVanOnsem, derived from the OP code, uses term unification when comparing the element to be removed with the elements of the list (an alternative would be to use term equality). % and increment the resulting index This is the rule that you want executed for each element of the list. Also, your definition of word_replacements/2 assumes the first argument is a list, but word_replacements(H, Replace_A) passes a non-list as the first argument. Whether the speed difference matters will depend on how often you need to do such a replacement It's slower: using a list of 10 million elements, and replacing the last one, then your second version takes 2. Transposing a matrix in Prolog using decompose. ?- L = [a, b, c, a, c, d], remove_elements(c, L, Result). Looping through and modifying a separate list in Prolog. I have a list of list and a list. This will never be the case, since you add X1 to the list before calling do_list/2 recursively. So first, you need to make a decision about the empty list. Prolog - Change elements of a list Prolog: replace an element in a list at a specified index. 0. We will discuss the methods and the actual commands that should be used and how to program them. same nesting) as OldList. I want the predicate to be a list and probably there's a way to do this better, but here's a working solution: (SWI prolog) %List of tuples, keeps track of the number of repetitions. In that case you have to compare the heads this is where concatenation should happen, right ? That would be a concatenation in reverse order, though. Check out my answer to the related question "How to count number of element occurrences in a list in Prolog"!In that answer I present the predicate list_counts/2, which should fot your needs. select(X, L, L_X), \+member(X, L_X) In Prolog exist predicates that collect element with a certain property setof/3 and bagof/3. True when Elem is the N’th (0-based) element of List and Rest is the remainder (as in by select A typical use for this predicate is to replace an element, as shown in the example below. If you want to learn Prolog, stick to the pure declarative subset first. Replace elements in lists of list prolog. So the following is true: memberCheckSimple([H|T], H). We can delete the Nth element by counting down from N repeatedly until the list is empty. removeAll(X, [X|T], L Your problem is that you are pulling items off the list 1 at a time. Using lists of lists usually hints at a bad representation. update nth element of a list. You have the special case of the empty list: replace( [] , _ , [] ) . Sample use::- list_counts([a,b,a,d,c,a,b],Ys). Hot Network Questions Confused about what an orbit means now Can there exist a definable "ultrafilter" on the ordinals? Obtaining the first elements. Deleting unwanted elements from list in PROLOG. There are two problems here: appending [(H1, H2)] and [] gives us a result that we can know in advance: Y will be [(H1, H2)] as well;; you do not do anything with the tail X in this case, so you only process the first element, and then throw away that element. In replace_multiple/2, the call to replace/4 has Lst on first and second position. anna April 20, 2022, 1:56pm 1. It works, but my question is can this rule be written otherwise: elemen In general, we try to start by the most basic set, the empty one, so replace "step 1" that becames now: the sum of the elements of an empty set is 0: sum([],0). L2 = [[1,0,5],[8,2,0],[0,0,9]]. Count the number of a specific object element in Prolog. Prolog I am trying to achieve this: Given OldList, replace any item if the item fulfills a goal (oldNew); if not, do not replace the item. Hi sorry I'm really new to Prolog. 3) Finally because all clause require at least two elements your base of recursion is the list with one element : remove_duplicates2([H],[H]). /* H is a member of [H|T] */ It's also true that an element is a I am trying to write a Prolog code finding the n-th element of a list. Replace a single occurrence of an element in a list in Prolog. The answer looks approximately insert(Src,X,Y,Tar) :- get(Src,X,Foo),replace(Foo,Y, Bar),replace(Src,X,Bar) Prolog - Change elements of a list. 0 seconds on my machine, fortran's version uses 1. You know that if the element is at the head of the list, that it is an element of the list. Hot Network Questions Can you attempt a risky task without risking your mind or body? Can I bring candles on an European flight? Is it a good idea to immerse the circuit in an engineered fluid in order [det] nth0(?N, ?List, ?Elem, ?Rest) Select/insert element at index. Element manipulation in Prolog. \2, where the first (leftmost) argument is the head of the list and the second (rightmost) argument is the tail of the list, which is, recursively, itself a list. How to find the index for a given item in a list? Replacing elements in list of lists PROLOG. A typical use for this predicate is to replace an element, as shown in the example below. This predicate is re-executable on backtracking and can be thus used to enumerate the elements of List . replace(E,S,[],[]). But can result in unexpected results when the terms are not ground. Prolog: replace an element in a list at a specified index. Follow edited Mar 14, 2016 at 23:25. Count specific element in list [Prolog] 4. Replace The first clause (base case) unifies the second argument with the empty list when there is only one element in the first argument list. But the output is always true Prolog: replace an element in a list at a specified index. logical variables. For example, I have the list [1,2,rep,3,4,5] and I want to end up with [1,2,2,3,4,5 Prolog - replacing list elements. compatible(_,[]). Errors List is type-checked. L, then I compare every element of L with A and if they're the same, I can change it to V. Prolog - remove from a list all repetitive elements (only keep unique elements) 12. List may contain variables. 10. the idea is simple, if the elements match, change it, if not, go forward until empty. , you don't have a recursion anchor, and the goal ?- do_list(5,L) will never return. We can however define constraints between these elements, and as a result, we can query in several directions::- use_module(library(clpfd)). The third problem is that you add X1 to the list instead of X. replace an element in list with its first occurence but keep replacing for all occurences- Prolog. For example: I have a list of list [[banan,NA],[apple,NA]] and a list [sweet,notsweet], want to update the list of the list, so I will have a list of list [[banana,sweet],[apple,notsweet]] You could (1) reverse the list, remove the head, then reverse again, or (2) use the append/3 predicate (hint: use the last element of the list as a single element list for the second argument), or (3) write a simple recursion that omits the last element when you get to the end (hint: a base case would be remove_last([_], ?) what would ? be?). See also - sort/2 can be used to create an ordered set I think you need to define the first clause of replaceX with: replaceX(A,_,0,_,A):-!. say i have two lists of lists eg: L1 = [[_,_,_],[_,_,_],[_,_,_]. When parameter X is already instantiated then L will be either the list [X] if X is contained in input parameter Y , of it will fail if X is not contained in Y . In other words, replace_elements([], [], _, _) says that when you replace the elements in an empty list with elements in another empty list, you can get anything you want from anything you want (!), which isn't logical. Example: L = [1,2 I’ve just seen this length/2 definition on stackoverflow also. About; Products OverflowAI; Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI Prolog replace element in a list with another list. So they don't serve any purpose. Prolog adding and removing list element if non present in second list. Why does the MS-DOS 4. E. When the tail list is not empty, the second clause of dosomething would unify with the shorter list to continue processing. I want to use recurrsion for this. I need do this: replace(L,P,E,R), where L is the current list, P is the position where the element will be insert, E is the element to insert and R is the return, the new list. How to replace every occurence of a value with another one in a binary tree with Prolog. Prolog - replacing list elements. And, if you only want the times when more than one teacher co-occur in the teaching schedule, you can simply remove the initial vars X and Y, and even replace R with the final result itself, just as follows: list; prolog; element; Share. Is there an easy way to do this? We transform a and m into a list of pairs (element from a, element from m), and iterate over the pairs. which is simply telling you what teachers X and Y teaches both at the same time B, as returned in the list R. I have the following code: my_delete(X, L, R):- [] = L, [] = R my_delete(X, L, R):- What you should do in Prolog is make your recursive swap call return Nlist1 and then use Nlist1 to compute Nlist. my problem is how to remove first elements of a list until an element (first occurrence). Prolog copy a specific letter from a list to another in the same place. e. Improve this answer. One issue is that your base case uses anonymous variables (_) in places you should have a specific value or regular variable. Swap last two elements of a list in Prolog. Ask Question Asked 9 years, 8 months ago. This is the rule that you want executed for each element of the list. Replace elements of a list in Prolog. The second clause states that when the first argument is a list with at least two elements, then you recursively call itself (without the head), an add the Head to the second argument returned by that call. Prolog how to delete from a list of lists. First the index of where you want to replace, this is starting I need do this: replace(L,P,E,R), where L is the current list, P is the position where the element will be insert, E is the element to insert and R is the return, the new list. I can't seem to replace, for instance, a g(X) in [s(f(a,b,g(X))]. % We found the element indexOf([_|Tail], Element, Index):- indexOf(Tail, Element, Index1), % Check in the tail of the list Index is Index1+1. ?- replace([1,2,3,4,5],3,L,Z). In replace_multiple/2, the new element is described as Elem in the head, but as Letter in the body. Given the list [1, 2, 3, 4], display the last element. . Replace the elements in a If A is a first element, a middle list, and a last element, then B is the last element, the same middle list, Swap second and prelast element from a list prolog. True when Set has the same elements as List in the same order. When the tail list is empty, the first clause would unify, thus ending the Prolog recursively replace elements of list with elements of another list. Replace the elements in a list by different variables, prolog. I'd like to have a Prolog predicate that can replace an element in a list at a specified index. For example, if i have the list [1,2,3,4,5] I am trying to write two predicates. I am using only one parameter and using recursion. At least for me, if I just replace Y is 1+Z with succ(Z, Y), then I don't need the countall/3 predicate at all to get all solutions upon backtracking. Replacing elements in list of I need a method to replace one list containing numbers with a new list and returning the all matrix with the value replaced. bagof collect all the elements, setof keeps only one element. Replace a list in prolog. Here's what i came up with so far. The pattern [A, _] in your clause is wrong, or at at least not generic enough. match([Elem|Tail],Num,C, Substitute all variables you do not use by underscores _. I get it to work (see my code) for the special case OldList = [a, b, c] but I would like to write a predicate that generalizes across list lengths and nested A non-empty list is represented by the term . % add_tail(+List,+Element,-List) % Add the given element to the end of the list, without using the "append" predicate. Return a NewList with replaced items that has the same structure (i. So Prolog takes each item out of the list and prints it. Cause you are building a recursive predicate, deleting every element in the Head of the target list that match a specific element, until the list is empty. 5k 13 13 gold badges 109 109 silver badges 215 215 bronze badges. I have made use of this and recuresed overs You probably saw warnings about Replace_A and Replace_E being singleton variables. ; Your predicate will thus just process the first element, and create a list with that tuple, like: Replace elements of a list in Prolog. Need to remove last but one element in prolog. That means no cuts, and no side-effects. deleteOne(Term, [Term|Tail], Result) :- deleteOne("", Tail, Result), !. Removing first elements of a list in Prolog. Edited, correcting the mistake pointed out by @CapelliC, where predicate would succeed on N = 0. member(Element, List) succeeds if Element belongs to the List. You need to review This is a user’s guide to list processing in prolog programming. If it's the latter, you can replace check_element/2 with a form of maplist. Clauses #2 is a bit confusing. I am trying to write a predicate that follows some simple conditions. replace(E,S,[E|T1],[S|T2]):-replace(E,S,T1,T2). I wrote the below code but it doesn't return the element right. Prolog - Find second and second last elements in list. replacing terms in a list prolog. Example: % replace(+List,+Index,+Value,-NewList). So in basic pseudo - list of elements - computer, mouse, keyboard, webcam The goal length/2 in the calling predicate list_1s/2 together with the 4th argument of the actual relation list_1s_/4 is used to make sure the result lists are listed in a fair manner if the predicate is called with the first argument being variable. Here is the same split implemented as a DCG, with basically the same performance as split_list_into_lens/3 (the cut increases performance): Verbally, the fail forces Prolog to back up to the last choice point it made and try using the next solution. tr(A,B,L,M) if list M is the same as list L, except that every occurrence of A in L is replaced by B. how do i compare the two lists of lists I am trying to create a predicate in Prolog which allows me to delete all occurrences of X in a list L. OK, now here is an idea of solving your problem. Well you can apply the same trick for your clist/2 predicate: instead of solving the problem for lists with two elements, you can consider two cases:. 81 1 1 gold badge Your problem is that you are pulling items off the list 1 at a time. Second clause, if the element is the Head of the List, don't copy it to the Result list, and continue the recursive call with the Tail. Replace the Engine, rebuild, or just put on new rings A professor I don't know is asking me (a high school graduate) to Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company The second is that the second clause only matches if the input list is empty. Stack Overflow. If I have a list. Improve this question. I did one part but I am struggling to get the other part working. says that if A = [X | Y] is a non-empty list to append to B = Z, and if W is Y appended to Z, then R = [X | W]. I'll steal borrow liberally from CapelliC's excellent answer to the base question and add in the key tabulation logic: % Key not present, then it goes in with count 1 place_key(Key, [], [Key-1]). This is what I tried. I am trying to duplicate the element of a list before the "rep" element, in a NON-recursive way. Prolog: How does delete/3 works? 1. The left-most copy of duplicate elements is retained. Prolog - Change elements of a list. All possible substitutions are performed on backtracking. Well, write/1 and nl/0 don't produce choice points because they only have one solution, but member/2 does have multiple solutions—one for each item in the list. For example: I have a list of list [[banan,NA],[apple,NA]] and a list [sweet,notsweet], want to update the list of the list, so I will have a list of list [[banana,sweet],[apple,notsweet]] Prolog: replace an element in a list at a specified index. It should take 2 lists and 2 variables and should return true if the first variable is located at the same position in the first list as the second variable is located in the second list. To remove a single element in a list there is a library function 'delete/3' which take in a list and an item you want to remove from that list and returns the new list with the item removed. I need to remove the first element from a list (the head). It appears that there is no add but there is union/3 so you can add elements by intersecting with a set of the new element (intersection([NewEl], OldSet, NewSet). Prolog - Give out every nth element of a list. D is the set of elements of the list which appears only one time. So a predicate that implements what you want should have (at least) four arguments: - the position of the % replace_element_at(+Index, +List, +Elem, ?NewList). The cut, on the other hand, helps you get rid of undesired backtracking. Replace the Engine, rebuild, or just put on new rings 40s-50s short story about a man who gets aliens to solve problems What I want is to create a function that will compare elements of one list to the elements of other list. Assuming this is somewhat correct, I'm running into problems with nested compounds, i. So this clause is logically incorrect. Here's an explanation. Iterate by recursion and decrement the value of the number of element each time; Removing first elements of a list in Prolog. Here this is for instance: compatible([],_). If you replace an element in a list with a different value, the result is a different list. replacing multiple terms from a list in prolog. mqxyq nhhj yvz fegml wyy cckm aksw vgae prbndg nqcl