Changing the elements of the list based on subscripts












2












$begingroup$


Say I have a list of lists: 



{{Subscript[a,1],Subscript[a,1]+Subscript[a,2],Subscript[a,-3]},

 {Subscript[a,1],Subscript[a,-2],Subscript[a,-4]}}


Now, in the sublists of that list, if an element has a negative subscript I want to change this element to a negative of that element with a positive subscript, so if I applied this to the list above I'd get:



{{Subscript[a,1],Subscript[a,1]+Subscript[a,2],-Subscript[a,3]},

 {Subscript[a,1],-Subscript[a,2],-Subscript[a,4]}}


I don't really know how to do it. Any help would be much appreciated.






list-manipulation subscript







share|improve this question









$endgroup$

















    2












    $begingroup$


    Say I have a list of lists: 



    {{Subscript[a,1],Subscript[a,1]+Subscript[a,2],Subscript[a,-3]},
    
 {Subscript[a,1],Subscript[a,-2],Subscript[a,-4]}}


    Now, in the sublists of that list, if an element has a negative subscript I want to change this element to a negative of that element with a positive subscript, so if I applied this to the list above I'd get:



    {{Subscript[a,1],Subscript[a,1]+Subscript[a,2],-Subscript[a,3]},
    
 {Subscript[a,1],-Subscript[a,2],-Subscript[a,4]}}


    I don't really know how to do it. Any help would be much appreciated.






    list-manipulation subscript







    share|improve this question









    $endgroup$















      2












      2








      2





      $begingroup$


      Say I have a list of lists: 



      {{Subscript[a,1],Subscript[a,1]+Subscript[a,2],Subscript[a,-3]},
      
 {Subscript[a,1],Subscript[a,-2],Subscript[a,-4]}}


      Now, in the sublists of that list, if an element has a negative subscript I want to change this element to a negative of that element with a positive subscript, so if I applied this to the list above I'd get:



      {{Subscript[a,1],Subscript[a,1]+Subscript[a,2],-Subscript[a,3]},
      
 {Subscript[a,1],-Subscript[a,2],-Subscript[a,4]}}


      I don't really know how to do it. Any help would be much appreciated.






      list-manipulation subscript







      share|improve this question









      $endgroup$




      Say I have a list of lists: 



      {{Subscript[a,1],Subscript[a,1]+Subscript[a,2],Subscript[a,-3]},
      
 {Subscript[a,1],Subscript[a,-2],Subscript[a,-4]}}


      Now, in the sublists of that list, if an element has a negative subscript I want to change this element to a negative of that element with a positive subscript, so if I applied this to the list above I'd get:



      {{Subscript[a,1],Subscript[a,1]+Subscript[a,2],-Subscript[a,3]},
      
 {Subscript[a,1],-Subscript[a,2],-Subscript[a,4]}}


      I don't really know how to do it. Any help would be much appreciated.






      list-manipulation subscript




      list-manipulation subscript






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      asked 14 hours ago









      amator2357amator2357

      1117




      1117






















          1 Answer
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          $begingroup$

          You can use pattern matching for this:



          expr = {{Subscript[a, 1], Subscript[a, 1] + Subscript[a, 2],    Subscript[a, -3]}, {Subscript[a, 1], Subscript[a, -2], Subscript[a, -4]}}
          

          
expr /. Subscript[a, n_Integer /; n < 0] :> - Subscript[a, -n]





          share|improve this answer









          $endgroup$













          • $begingroup$
            I was just looking at pattern matching :) Thank you very much @Fred Simons .
            $endgroup$
            – amator2357
            14 hours ago











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          1 Answer
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          1 Answer
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          active

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          active

          oldest

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          active

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          4












          $begingroup$

          You can use pattern matching for this:



          expr = {{Subscript[a, 1], Subscript[a, 1] + Subscript[a, 2],    Subscript[a, -3]}, {Subscript[a, 1], Subscript[a, -2], Subscript[a, -4]}}
          

          
expr /. Subscript[a, n_Integer /; n < 0] :> - Subscript[a, -n]





          share|improve this answer









          $endgroup$













          • $begingroup$
            I was just looking at pattern matching :) Thank you very much @Fred Simons .
            $endgroup$
            – amator2357
            14 hours ago
















          4












          $begingroup$

          You can use pattern matching for this:



          expr = {{Subscript[a, 1], Subscript[a, 1] + Subscript[a, 2],    Subscript[a, -3]}, {Subscript[a, 1], Subscript[a, -2], Subscript[a, -4]}}
          

          
expr /. Subscript[a, n_Integer /; n < 0] :> - Subscript[a, -n]





          share|improve this answer









          $endgroup$













          • $begingroup$
            I was just looking at pattern matching :) Thank you very much @Fred Simons .
            $endgroup$
            – amator2357
            14 hours ago














          4












          4








          4





          $begingroup$

          You can use pattern matching for this:



          expr = {{Subscript[a, 1], Subscript[a, 1] + Subscript[a, 2],    Subscript[a, -3]}, {Subscript[a, 1], Subscript[a, -2], Subscript[a, -4]}}
          

          
expr /. Subscript[a, n_Integer /; n < 0] :> - Subscript[a, -n]





          share|improve this answer









          $endgroup$



          You can use pattern matching for this:



          expr = {{Subscript[a, 1], Subscript[a, 1] + Subscript[a, 2],    Subscript[a, -3]}, {Subscript[a, 1], Subscript[a, -2], Subscript[a, -4]}}
          

          
expr /. Subscript[a, n_Integer /; n < 0] :> - Subscript[a, -n]






          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered 14 hours ago









          Fred SimonsFred Simons

          7,1671241




          7,1671241












          • $begingroup$
            I was just looking at pattern matching :) Thank you very much @Fred Simons .
            $endgroup$
            – amator2357
            14 hours ago


















          • $begingroup$
            I was just looking at pattern matching :) Thank you very much @Fred Simons .
            $endgroup$
            – amator2357
            14 hours ago
















          $begingroup$
          I was just looking at pattern matching :) Thank you very much @Fred Simons .
          $endgroup$
          – amator2357
          14 hours ago




          $begingroup$
          I was just looking at pattern matching :) Thank you very much @Fred Simons .
          $endgroup$
          – amator2357
          14 hours ago


















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