Extracting specific data from a list

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Consider the following list



1., -1, 1.5, -1, 2., 1, 2.5, 1, 3., 1, 3.5, 1, 4., 1, 4.5, 1, 5., 1, 5.5, 1, 6., 1, 6.5, 1, 7., -1, 7.5, -1, 8., -1, 8.5, -1, 9., -1, 9.5, -1, 10., -1


How can I extract only the values after (or before) the second element in the 2-element sublists changes sign, i.e, I would like to obtain as a result



2., 1,7., -1





list-manipulation







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    up vote
    2
    down vote

    favorite












    Consider the following list



    1., -1, 1.5, -1, 2., 1, 2.5, 1, 3., 1, 3.5, 1, 4., 1, 4.5, 1, 5., 1, 5.5, 1, 6., 1, 6.5, 1, 7., -1, 7.5, -1, 8., -1, 8.5, -1, 9., -1, 9.5, -1, 10., -1


    How can I extract only the values after (or before) the second element in the 2-element sublists changes sign, i.e, I would like to obtain as a result



    2., 1,7., -1





    list-manipulation







    share|improve this question























      up vote
      2
      down vote

      favorite









      up vote
      2
      down vote

      favorite











      Consider the following list



      1., -1, 1.5, -1, 2., 1, 2.5, 1, 3., 1, 3.5, 1, 4., 1, 4.5, 1, 5., 1, 5.5, 1, 6., 1, 6.5, 1, 7., -1, 7.5, -1, 8., -1, 8.5, -1, 9., -1, 9.5, -1, 10., -1


      How can I extract only the values after (or before) the second element in the 2-element sublists changes sign, i.e, I would like to obtain as a result



      2., 1,7., -1





      list-manipulation







      share|improve this question













      Consider the following list



      1., -1, 1.5, -1, 2., 1, 2.5, 1, 3., 1, 3.5, 1, 4., 1, 4.5, 1, 5., 1, 5.5, 1, 6., 1, 6.5, 1, 7., -1, 7.5, -1, 8., -1, 8.5, -1, 9., -1, 9.5, -1, 10., -1


      How can I extract only the values after (or before) the second element in the 2-element sublists changes sign, i.e, I would like to obtain as a result



      2., 1,7., -1





      list-manipulation




      list-manipulation






      share|improve this question













      share|improve this question











      share|improve this question




      share|improve this question










      asked Aug 19 at 13:32









      jarhead

      689413




      689413




















          1 Answer
          1






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          First /@ Rest@SplitBy[list, Sign[#[[2]]] &]



          2., 1, 7., -1




          or



          First /@ Rest@Split[list, Sign[#[[2]]] == Sign[#2[[2]]] &]



          2., 1, 7., -1




          Also



          Pick[list, Developer`ToPackedArray[Unitize[Join[0, 
           Differences @ UnitStep @ Transpose[list][[2]]]]], 1]



          2., 1, 7., -1







          share|improve this answer






















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            1 Answer
            1






            active

            oldest

            votes








            1 Answer
            1






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes








            up vote
            5
            down vote



            accepted










            First /@ Rest@SplitBy[list, Sign[#[[2]]] &]



            2., 1, 7., -1




            or



            First /@ Rest@Split[list, Sign[#[[2]]] == Sign[#2[[2]]] &]



            2., 1, 7., -1




            Also



            Pick[list, Developer`ToPackedArray[Unitize[Join[0, 
             Differences @ UnitStep @ Transpose[list][[2]]]]], 1]



            2., 1, 7., -1







            share|improve this answer


























              up vote
              5
              down vote



              accepted










              First /@ Rest@SplitBy[list, Sign[#[[2]]] &]



              2., 1, 7., -1




              or



              First /@ Rest@Split[list, Sign[#[[2]]] == Sign[#2[[2]]] &]



              2., 1, 7., -1




              Also



              Pick[list, Developer`ToPackedArray[Unitize[Join[0, 
               Differences @ UnitStep @ Transpose[list][[2]]]]], 1]



              2., 1, 7., -1







              share|improve this answer
























                up vote
                5
                down vote



                accepted







                up vote
                5
                down vote



                accepted






                First /@ Rest@SplitBy[list, Sign[#[[2]]] &]



                2., 1, 7., -1




                or



                First /@ Rest@Split[list, Sign[#[[2]]] == Sign[#2[[2]]] &]



                2., 1, 7., -1




                Also



                Pick[list, Developer`ToPackedArray[Unitize[Join[0, 
                 Differences @ UnitStep @ Transpose[list][[2]]]]], 1]



                2., 1, 7., -1







                share|improve this answer














                First /@ Rest@SplitBy[list, Sign[#[[2]]] &]



                2., 1, 7., -1




                or



                First /@ Rest@Split[list, Sign[#[[2]]] == Sign[#2[[2]]] &]



                2., 1, 7., -1




                Also



                Pick[list, Developer`ToPackedArray[Unitize[Join[0, 
                 Differences @ UnitStep @ Transpose[list][[2]]]]], 1]



                2., 1, 7., -1








                share|improve this answer














                share|improve this answer



                share|improve this answer








                edited Aug 19 at 13:46

























                answered Aug 19 at 13:36









                kglr

                161k8185384




                161k8185384



























                     

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