Prolog length of a list












3















How can I calculate the length of a list



?- size_sub([[b,a,g], [9,3,7,4], [6]],  X).

X = [3, 4, 1].



?- size_sub([[c,g,e,w], [7]],  X).

X = [4, 1].



?- size_sub(,  X).

X = .





list prolog







share|improve this question




















  • 1





    is that last one correct? to be consistent wouldn't that be size_sub([],X). or size_sub(,X) the answer would be

    – Bob Vale
    Sep 15 '11 at 19:50


















3















How can I calculate the length of a list



?- size_sub([[b,a,g], [9,3,7,4], [6]],  X).

X = [3, 4, 1].



?- size_sub([[c,g,e,w], [7]],  X).

X = [4, 1].



?- size_sub(,  X).

X = .





list prolog







share|improve this question




















  • 1





    is that last one correct? to be consistent wouldn't that be size_sub([],X). or size_sub(,X) the answer would be

    – Bob Vale
    Sep 15 '11 at 19:50
















3












3








3


0






How can I calculate the length of a list



?- size_sub([[b,a,g], [9,3,7,4], [6]],  X).

X = [3, 4, 1].



?- size_sub([[c,g,e,w], [7]],  X).

X = [4, 1].



?- size_sub(,  X).

X = .





list prolog







share|improve this question
















How can I calculate the length of a list



?- size_sub([[b,a,g], [9,3,7,4], [6]],  X).

X = [3, 4, 1].



?- size_sub([[c,g,e,w], [7]],  X).

X = [4, 1].



?- size_sub(,  X).

X = .





list prolog




list prolog






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Jun 2 '15 at 9:44









repeat

14.7k441136




14.7k441136










asked Sep 15 '11 at 19:45









MaryMary

21113




21113








  • 1





    is that last one correct? to be consistent wouldn't that be size_sub([],X). or size_sub(,X) the answer would be

    – Bob Vale
    Sep 15 '11 at 19:50
















  • 1





    is that last one correct? to be consistent wouldn't that be size_sub([],X). or size_sub(,X) the answer would be

    – Bob Vale
    Sep 15 '11 at 19:50










1




1





is that last one correct? to be consistent wouldn't that be size_sub([],X). or size_sub(,X) the answer would be

– Bob Vale
Sep 15 '11 at 19:50







is that last one correct? to be consistent wouldn't that be size_sub([],X). or size_sub(,X) the answer would be

– Bob Vale
Sep 15 '11 at 19:50














2 Answers
2






active

oldest

votes


















7














To map length/2 over a list of lists, we can use the meta-predicate maplist/3 like this:



size_sub(Xss,Ls):-

    maplist(length,Xss,Ls).





share|improve this answer

































    6














    Ok you need to start with the base case which is the last answer



    so size_sub(,X). is true if X= so first you write that as a rule.



    size_sub(,).


    Then you need to do the inductive step a list that is one longer than the previous. I am going to assume that you have a size/2 function for determining the size of a single list (if not please comment).



    So the inductive step is going to operate on the length of the first parameter so N->N+1. We would represent this by striping off the head of the list syntax will be [H|T] now the second parameter (your answer) is going to be the length of H with the result of calling size_sub on T. As we cannot specify rules in the parameters in the header we will use N to represent the length of H and T2 to represent the result of size_sub on T.



    So the first part of the rule becomes size_sub([H|T],[N|T2]):-



    now we follow it with the predicates that will assert the values for N and T2.



    size(H,N),
    
size_sub(T,T2).


    putting that all together you get



    size_sub(,).
    

    
size_sub([H|T],[N|T2]):-
    
    size(H,N),
    
    size_sub(T,T2).


    size/2 is a far simpler case and following the same process of base + inductive you should be able to create the rules for it. Please comment if you need further help.



    ** EDIT - Request for size/2 definition **



    To define size/2



    Start with the base case, the empty list has a size of 0.



    size(,0).


    Now the inductive step. The size of list of length(N+1) is the size of a list of length(N). So lets define our list as [_|T] I've defined the list using _ to represent the head because we never use it so we can just use the anonymous variable. Lets use N to represent the length of T, and M to be N+1.



    so



    size([_|T],M):-



    now lets define N



      size(T,N),


    and finally assert that M is equal to N + 1



      M is N+1.


    so putting everything together



    size(,0).
    

    
size([_|T],N):-
    
    size(T,M),
    
    N is M+1.
    

    
size_sub(,).
    

    
size_sub([H|T],[N|T2]):-
    
    size(H,N),
    
    size_sub(T,T2).





    share|improve this answer


























    • I don't know how to create size/2

      – Mary
      Sep 15 '11 at 20:24











    • @Mary answer updated

      – Bob Vale
      Sep 15 '11 at 22:37











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    2 Answers
    2






    active

    oldest

    votes








    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    7














    To map length/2 over a list of lists, we can use the meta-predicate maplist/3 like this:



    size_sub(Xss,Ls):-
    
    maplist(length,Xss,Ls).





    share|improve this answer






























      7














      To map length/2 over a list of lists, we can use the meta-predicate maplist/3 like this:



      size_sub(Xss,Ls):-
      
    maplist(length,Xss,Ls).





      share|improve this answer




























        7












        7








        7







        To map length/2 over a list of lists, we can use the meta-predicate maplist/3 like this:



        size_sub(Xss,Ls):-
        
    maplist(length,Xss,Ls).





        share|improve this answer















        To map length/2 over a list of lists, we can use the meta-predicate maplist/3 like this:



        size_sub(Xss,Ls):-
        
    maplist(length,Xss,Ls).






        share|improve this answer














        share|improve this answer



        share|improve this answer








        edited May 23 '17 at 10:27









        Community♦

        11




        11










        answered Sep 16 '11 at 11:18









        Thanos TintinidisThanos Tintinidis

        5,38511229




        5,38511229

























            6














            Ok you need to start with the base case which is the last answer



            so size_sub(,X). is true if X= so first you write that as a rule.



            size_sub(,).


            Then you need to do the inductive step a list that is one longer than the previous. I am going to assume that you have a size/2 function for determining the size of a single list (if not please comment).



            So the inductive step is going to operate on the length of the first parameter so N->N+1. We would represent this by striping off the head of the list syntax will be [H|T] now the second parameter (your answer) is going to be the length of H with the result of calling size_sub on T. As we cannot specify rules in the parameters in the header we will use N to represent the length of H and T2 to represent the result of size_sub on T.



            So the first part of the rule becomes size_sub([H|T],[N|T2]):-



            now we follow it with the predicates that will assert the values for N and T2.



            size(H,N),
            
size_sub(T,T2).


            putting that all together you get



            size_sub(,).
            

            
size_sub([H|T],[N|T2]):-
            
    size(H,N),
            
    size_sub(T,T2).


            size/2 is a far simpler case and following the same process of base + inductive you should be able to create the rules for it. Please comment if you need further help.



            ** EDIT - Request for size/2 definition **



            To define size/2



            Start with the base case, the empty list has a size of 0.



            size(,0).


            Now the inductive step. The size of list of length(N+1) is the size of a list of length(N). So lets define our list as [_|T] I've defined the list using _ to represent the head because we never use it so we can just use the anonymous variable. Lets use N to represent the length of T, and M to be N+1.



            so



            size([_|T],M):-



            now lets define N



              size(T,N),


            and finally assert that M is equal to N + 1



              M is N+1.


            so putting everything together



            size(,0).
            

            
size([_|T],N):-
            
    size(T,M),
            
    N is M+1.
            

            
size_sub(,).
            

            
size_sub([H|T],[N|T2]):-
            
    size(H,N),
            
    size_sub(T,T2).





            share|improve this answer


























            • I don't know how to create size/2

              – Mary
              Sep 15 '11 at 20:24











            • @Mary answer updated

              – Bob Vale
              Sep 15 '11 at 22:37
















            6














            Ok you need to start with the base case which is the last answer



            so size_sub(,X). is true if X= so first you write that as a rule.



            size_sub(,).


            Then you need to do the inductive step a list that is one longer than the previous. I am going to assume that you have a size/2 function for determining the size of a single list (if not please comment).



            So the inductive step is going to operate on the length of the first parameter so N->N+1. We would represent this by striping off the head of the list syntax will be [H|T] now the second parameter (your answer) is going to be the length of H with the result of calling size_sub on T. As we cannot specify rules in the parameters in the header we will use N to represent the length of H and T2 to represent the result of size_sub on T.



            So the first part of the rule becomes size_sub([H|T],[N|T2]):-



            now we follow it with the predicates that will assert the values for N and T2.



            size(H,N),
            
size_sub(T,T2).


            putting that all together you get



            size_sub(,).
            

            
size_sub([H|T],[N|T2]):-
            
    size(H,N),
            
    size_sub(T,T2).


            size/2 is a far simpler case and following the same process of base + inductive you should be able to create the rules for it. Please comment if you need further help.



            ** EDIT - Request for size/2 definition **



            To define size/2



            Start with the base case, the empty list has a size of 0.



            size(,0).


            Now the inductive step. The size of list of length(N+1) is the size of a list of length(N). So lets define our list as [_|T] I've defined the list using _ to represent the head because we never use it so we can just use the anonymous variable. Lets use N to represent the length of T, and M to be N+1.



            so



            size([_|T],M):-



            now lets define N



              size(T,N),


            and finally assert that M is equal to N + 1



              M is N+1.


            so putting everything together



            size(,0).
            

            
size([_|T],N):-
            
    size(T,M),
            
    N is M+1.
            

            
size_sub(,).
            

            
size_sub([H|T],[N|T2]):-
            
    size(H,N),
            
    size_sub(T,T2).





            share|improve this answer


























            • I don't know how to create size/2

              – Mary
              Sep 15 '11 at 20:24











            • @Mary answer updated

              – Bob Vale
              Sep 15 '11 at 22:37














            6












            6








            6







            Ok you need to start with the base case which is the last answer



            so size_sub(,X). is true if X= so first you write that as a rule.



            size_sub(,).


            Then you need to do the inductive step a list that is one longer than the previous. I am going to assume that you have a size/2 function for determining the size of a single list (if not please comment).



            So the inductive step is going to operate on the length of the first parameter so N->N+1. We would represent this by striping off the head of the list syntax will be [H|T] now the second parameter (your answer) is going to be the length of H with the result of calling size_sub on T. As we cannot specify rules in the parameters in the header we will use N to represent the length of H and T2 to represent the result of size_sub on T.



            So the first part of the rule becomes size_sub([H|T],[N|T2]):-



            now we follow it with the predicates that will assert the values for N and T2.



            size(H,N),
            
size_sub(T,T2).


            putting that all together you get



            size_sub(,).
            

            
size_sub([H|T],[N|T2]):-
            
    size(H,N),
            
    size_sub(T,T2).


            size/2 is a far simpler case and following the same process of base + inductive you should be able to create the rules for it. Please comment if you need further help.



            ** EDIT - Request for size/2 definition **



            To define size/2



            Start with the base case, the empty list has a size of 0.



            size(,0).


            Now the inductive step. The size of list of length(N+1) is the size of a list of length(N). So lets define our list as [_|T] I've defined the list using _ to represent the head because we never use it so we can just use the anonymous variable. Lets use N to represent the length of T, and M to be N+1.



            so



            size([_|T],M):-



            now lets define N



              size(T,N),


            and finally assert that M is equal to N + 1



              M is N+1.


            so putting everything together



            size(,0).
            

            
size([_|T],N):-
            
    size(T,M),
            
    N is M+1.
            

            
size_sub(,).
            

            
size_sub([H|T],[N|T2]):-
            
    size(H,N),
            
    size_sub(T,T2).





            share|improve this answer















            Ok you need to start with the base case which is the last answer



            so size_sub(,X). is true if X= so first you write that as a rule.



            size_sub(,).


            Then you need to do the inductive step a list that is one longer than the previous. I am going to assume that you have a size/2 function for determining the size of a single list (if not please comment).



            So the inductive step is going to operate on the length of the first parameter so N->N+1. We would represent this by striping off the head of the list syntax will be [H|T] now the second parameter (your answer) is going to be the length of H with the result of calling size_sub on T. As we cannot specify rules in the parameters in the header we will use N to represent the length of H and T2 to represent the result of size_sub on T.



            So the first part of the rule becomes size_sub([H|T],[N|T2]):-



            now we follow it with the predicates that will assert the values for N and T2.



            size(H,N),
            
size_sub(T,T2).


            putting that all together you get



            size_sub(,).
            

            
size_sub([H|T],[N|T2]):-
            
    size(H,N),
            
    size_sub(T,T2).


            size/2 is a far simpler case and following the same process of base + inductive you should be able to create the rules for it. Please comment if you need further help.



            ** EDIT - Request for size/2 definition **



            To define size/2



            Start with the base case, the empty list has a size of 0.



            size(,0).


            Now the inductive step. The size of list of length(N+1) is the size of a list of length(N). So lets define our list as [_|T] I've defined the list using _ to represent the head because we never use it so we can just use the anonymous variable. Lets use N to represent the length of T, and M to be N+1.



            so



            size([_|T],M):-



            now lets define N



              size(T,N),


            and finally assert that M is equal to N + 1



              M is N+1.


            so putting everything together



            size(,0).
            

            
size([_|T],N):-
            
    size(T,M),
            
    N is M+1.
            

            
size_sub(,).
            

            
size_sub([H|T],[N|T2]):-
            
    size(H,N),
            
    size_sub(T,T2).






            share|improve this answer














            share|improve this answer



            share|improve this answer








            edited Sep 15 '11 at 20:34

























            answered Sep 15 '11 at 20:10









            Bob ValeBob Vale

            15.7k2742




            15.7k2742













            • I don't know how to create size/2

              – Mary
              Sep 15 '11 at 20:24











            • @Mary answer updated

              – Bob Vale
              Sep 15 '11 at 22:37



















            • I don't know how to create size/2

              – Mary
              Sep 15 '11 at 20:24











            • @Mary answer updated

              – Bob Vale
              Sep 15 '11 at 22:37

















            I don't know how to create size/2

            – Mary
            Sep 15 '11 at 20:24





            I don't know how to create size/2

            – Mary
            Sep 15 '11 at 20:24













            @Mary answer updated

            – Bob Vale
            Sep 15 '11 at 22:37





            @Mary answer updated

            – Bob Vale
            Sep 15 '11 at 22:37


















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