Haskell - Sort List of Tuples by the Last Tuple Element [duplicate]












-1















This question already has an answer here:




  • sorting lists using sortBy

    2 answers




I have been trying to find a way to sort a list [(a,b,c,d),(e,f,g,h)] by the d element.



So far I have tried: sortBy (compare on snd) but I cant find a way to get the 4th element and not the 2nd.



My output has to be the same but ordered instead.



Thanks in advance!






haskell







share|improve this question













marked as duplicate by jberryman, Community♦ Nov 23 at 10:23


This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.




















    -1















    This question already has an answer here:




    • sorting lists using sortBy

      2 answers




    I have been trying to find a way to sort a list [(a,b,c,d),(e,f,g,h)] by the d element.



    So far I have tried: sortBy (compare on snd) but I cant find a way to get the 4th element and not the 2nd.



    My output has to be the same but ordered instead.



    Thanks in advance!






    haskell







    share|improve this question













    marked as duplicate by jberryman, Community♦ Nov 23 at 10:23


    This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.


















      -1












      -1








      -1








      This question already has an answer here:




      • sorting lists using sortBy

        2 answers




      I have been trying to find a way to sort a list [(a,b,c,d),(e,f,g,h)] by the d element.



      So far I have tried: sortBy (compare on snd) but I cant find a way to get the 4th element and not the 2nd.



      My output has to be the same but ordered instead.



      Thanks in advance!






      haskell







      share|improve this question














      This question already has an answer here:




      • sorting lists using sortBy

        2 answers




      I have been trying to find a way to sort a list [(a,b,c,d),(e,f,g,h)] by the d element.



      So far I have tried: sortBy (compare on snd) but I cant find a way to get the 4th element and not the 2nd.



      My output has to be the same but ordered instead.



      Thanks in advance!





      This question already has an answer here:




      • sorting lists using sortBy

        2 answers







      haskell




      haskell






      share|improve this question













      share|improve this question











      share|improve this question




      share|improve this question










      asked Nov 22 at 18:34









      Ceut

      64




      64




      marked as duplicate by jberryman, Community♦ Nov 23 at 10:23


      This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.






      marked as duplicate by jberryman, Community♦ Nov 23 at 10:23


      This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.


























          2 Answers
          2






          active

          oldest

          votes


















          6














          fst and snd are provided specifically for 2-tuples as convenience functions. However, you can very easily write a function that works for 4-tuples.



          frth :: (a, b, c, d) -> d
          
frth (_, _, _, d) = d


          Then



          sortBy (compare `on` frth)





          share|improve this answer





















          • Thank you so much!
            – Ceut
            Nov 22 at 21:42










          • Or just sortOn frth.
            – Alec
            Nov 22 at 23:57










          • sortBy (compare `on` f) = sortBy (comparing f) = sortOn f
            – Jon Purdy
            Nov 23 at 7:17



















          4














          You can define your own projection



          get4thOf4 :: (a,b,c,d) -> d
          
get4thOf4 (_,_,_,d) = d


          after which you can use sortBy (comparing get4thof4).



          Alternatively, use a lambda: sortBy (comparing ((_,_,_,d) -> d))



          (comparing ... means the same thing as compare `on` ...)






          share|improve this answer




























            2 Answers
            2






            active

            oldest

            votes








            2 Answers
            2






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes









            6














            fst and snd are provided specifically for 2-tuples as convenience functions. However, you can very easily write a function that works for 4-tuples.



            frth :: (a, b, c, d) -> d
            
frth (_, _, _, d) = d


            Then



            sortBy (compare `on` frth)





            share|improve this answer





















            • Thank you so much!
              – Ceut
              Nov 22 at 21:42










            • Or just sortOn frth.
              – Alec
              Nov 22 at 23:57










            • sortBy (compare `on` f) = sortBy (comparing f) = sortOn f
              – Jon Purdy
              Nov 23 at 7:17
















            6














            fst and snd are provided specifically for 2-tuples as convenience functions. However, you can very easily write a function that works for 4-tuples.



            frth :: (a, b, c, d) -> d
            
frth (_, _, _, d) = d


            Then



            sortBy (compare `on` frth)





            share|improve this answer





















            • Thank you so much!
              – Ceut
              Nov 22 at 21:42










            • Or just sortOn frth.
              – Alec
              Nov 22 at 23:57










            • sortBy (compare `on` f) = sortBy (comparing f) = sortOn f
              – Jon Purdy
              Nov 23 at 7:17














            6












            6








            6






            fst and snd are provided specifically for 2-tuples as convenience functions. However, you can very easily write a function that works for 4-tuples.



            frth :: (a, b, c, d) -> d
            
frth (_, _, _, d) = d


            Then



            sortBy (compare `on` frth)





            share|improve this answer












            fst and snd are provided specifically for 2-tuples as convenience functions. However, you can very easily write a function that works for 4-tuples.



            frth :: (a, b, c, d) -> d
            
frth (_, _, _, d) = d


            Then



            sortBy (compare `on` frth)






            share|improve this answer












            share|improve this answer



            share|improve this answer










            answered Nov 22 at 18:44









            Silvio Mayolo

            13.6k22252




            13.6k22252












            • Thank you so much!
              – Ceut
              Nov 22 at 21:42










            • Or just sortOn frth.
              – Alec
              Nov 22 at 23:57










            • sortBy (compare `on` f) = sortBy (comparing f) = sortOn f
              – Jon Purdy
              Nov 23 at 7:17


















            • Thank you so much!
              – Ceut
              Nov 22 at 21:42










            • Or just sortOn frth.
              – Alec
              Nov 22 at 23:57










            • sortBy (compare `on` f) = sortBy (comparing f) = sortOn f
              – Jon Purdy
              Nov 23 at 7:17
















            Thank you so much!
            – Ceut
            Nov 22 at 21:42




            Thank you so much!
            – Ceut
            Nov 22 at 21:42












            Or just sortOn frth.
            – Alec
            Nov 22 at 23:57




            Or just sortOn frth.
            – Alec
            Nov 22 at 23:57












            sortBy (compare `on` f) = sortBy (comparing f) = sortOn f
            – Jon Purdy
            Nov 23 at 7:17




            sortBy (compare `on` f) = sortBy (comparing f) = sortOn f
            – Jon Purdy
            Nov 23 at 7:17













            4














            You can define your own projection



            get4thOf4 :: (a,b,c,d) -> d
            
get4thOf4 (_,_,_,d) = d


            after which you can use sortBy (comparing get4thof4).



            Alternatively, use a lambda: sortBy (comparing ((_,_,_,d) -> d))



            (comparing ... means the same thing as compare `on` ...)






            share|improve this answer


























              4














              You can define your own projection



              get4thOf4 :: (a,b,c,d) -> d
              
get4thOf4 (_,_,_,d) = d


              after which you can use sortBy (comparing get4thof4).



              Alternatively, use a lambda: sortBy (comparing ((_,_,_,d) -> d))



              (comparing ... means the same thing as compare `on` ...)






              share|improve this answer
























                4












                4








                4






                You can define your own projection



                get4thOf4 :: (a,b,c,d) -> d
                
get4thOf4 (_,_,_,d) = d


                after which you can use sortBy (comparing get4thof4).



                Alternatively, use a lambda: sortBy (comparing ((_,_,_,d) -> d))



                (comparing ... means the same thing as compare `on` ...)






                share|improve this answer












                You can define your own projection



                get4thOf4 :: (a,b,c,d) -> d
                
get4thOf4 (_,_,_,d) = d


                after which you can use sortBy (comparing get4thof4).



                Alternatively, use a lambda: sortBy (comparing ((_,_,_,d) -> d))



                (comparing ... means the same thing as compare `on` ...)







                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered Nov 22 at 18:44









                chi

                72.9k280135




                72.9k280135















                    -

                    Popular posts from this blog

                    Berounka

                    Image
                    Berounka.mw-parser-output .entete.map{background-image:url("//upload.wikimedia.org/wikipedia/commons/7/7a/Picto_infobox_map.png")} Caractéristiques Longueur 139  km Bassin 8 861  km 2 Bassin collecteur Elbe Débit moyen ? Cours Source Confluence de la Mže et de la Radbuza · Localisation Pilsen · Altitude 305  m · Coordonnées 49° 45′ 13″ N, 13° 23′ 24″ E Confluence Vltava · Localisation Prague · Altitude 187  m · Coordonnées 49° 59′ 43″ N, 14° 24′ 04″ E Géographie Pays traversés   République tchèque modifier   La Berounka est une rivière de la République tchèque. Elle porte le nom de Mže depuis sa source en Allemagne près de la frontière jusqu'à sa confluence avec la Radbuza à Plzeň. Elle continue ensuite sous le nom de Berounka jusqu'à sa confluence avec la Vltava, près de Prague. La rivière est une destination prisée pour les amateurs de canoë, qui appréc...
                    Read more

                    Sphinx de Gizeh

                    Image
                    Pour les articles homonymes, voir Sphinx. Sphinx de Gizeh.mw-parser-output .entete.egypte-antique{background-image:url("//upload.wikimedia.org/wikipedia/commons/c/cc/Picto_infobox_ancient_Egypt.png")} Site d'Égypte antique Le visage du sphinx de Gizeh. Noms en arabe أبو الهول , Abou al-Hôl Localisation Région Basse-Égypte Coordonnées 29° 58′ 31″ nord, 31° 08′ 16″ est Géolocalisation sur la carte : Égypte Sphinx de Gizeh modifier   Le sphinx de Gizeh est la statue thérianthrope qui se dresse devant les grandes pyramides du plateau de Gizeh, en Basse-Égypte. Sculpture monumentale monolithique la plus grande du monde [ 1 ] avec 73,5 mètres de longueur, 14 mètres de largeur et 20,22 mètres de hauteur, elle représente un sphinx couchant. Réalisée vers -2500, elle serait attribuée à Djédefrê, l'un des pharaons de la IV e  dynastie, représentant son père le pharaon Khéops. Sommaire 1 Étymologie 2 Desc...
                    Read more

                    Different font size/position of beamer's navigation symbols template's content depending on regular/plain...

                    Image
                    3 Let's suppose I'd like to divert the navigation symbols template (e.g. in order replace them by the frame numbers, see this bug report ;) I would be facing troubles regarding the font size/position, depending on regular/plain frames, as shown by the following MCE. How could I get rid of these troubles? documentclass{beamer} usetheme{PaloAlto} setbeamertemplate{navigation symbols}{insertframenumber/inserttotalframenumber} begin{document} begin{frame} frametitle{A regular frame} end{frame} begin{frame}[plain] frametitle{A plain frame} end{frame} end{document} beamer header-footer share | improve this question asked Dec 10 '18 a...
                    Read more