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How to make a Python function that operates on two or more nested lists of the same shape?


Convert two lists into a dictionaryHow can I safely create a nested directory?How do I return multiple values from a function?How can I make a time delay in Python?How to remove an element from a list by index?How to make a chain of function decorators?How to make a flat list out of list of listsHow do I get the number of elements in a list?How do I concatenate two lists in Python?How can I reverse a list in Python?






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margin-bottom:0;









1















I would like to apply an arbitrary function to two or more nested lists of the same shape. For instance if my function is:



def add(a, b):
if "NULL" not in [a, b]:
return a + b
else:
return "NULL"


and my inputs are:



input1 = [[1, 2, "NULL"], [3, 4], [5, 6, 7, 8]]
input2 = [[9, 8, "NULL"], [7, 6], [5, 4, 3, 2]]


Then I would like the output to be



output = [[10, 10, "NULL"], [10, 10], [10, 10, 10, 10]]


The inputs will always be nested one level deep, but the outputs ideally should be anything (for instance it could be nested deeper if the function was a "concatenate(a, b)" function)










share|improve this question


























  • Will the lists only ever be nested one level deep?

    – Peter Collingridge
    Mar 28 at 21:08











  • @PeterCollingridge Yes, at least in the input stage (perhaps the output could be nested deeper depending on the function applied)

    – AAC
    Mar 28 at 21:24












  • If the lists are nested one level deep aways, why not [func(val) for val in list_of_lists] or event map(func, list_of_lists), it would simplify your function.

    – geckos
    Mar 28 at 21:30

















1















I would like to apply an arbitrary function to two or more nested lists of the same shape. For instance if my function is:



def add(a, b):
if "NULL" not in [a, b]:
return a + b
else:
return "NULL"


and my inputs are:



input1 = [[1, 2, "NULL"], [3, 4], [5, 6, 7, 8]]
input2 = [[9, 8, "NULL"], [7, 6], [5, 4, 3, 2]]


Then I would like the output to be



output = [[10, 10, "NULL"], [10, 10], [10, 10, 10, 10]]


The inputs will always be nested one level deep, but the outputs ideally should be anything (for instance it could be nested deeper if the function was a "concatenate(a, b)" function)










share|improve this question


























  • Will the lists only ever be nested one level deep?

    – Peter Collingridge
    Mar 28 at 21:08











  • @PeterCollingridge Yes, at least in the input stage (perhaps the output could be nested deeper depending on the function applied)

    – AAC
    Mar 28 at 21:24












  • If the lists are nested one level deep aways, why not [func(val) for val in list_of_lists] or event map(func, list_of_lists), it would simplify your function.

    – geckos
    Mar 28 at 21:30













1












1








1








I would like to apply an arbitrary function to two or more nested lists of the same shape. For instance if my function is:



def add(a, b):
if "NULL" not in [a, b]:
return a + b
else:
return "NULL"


and my inputs are:



input1 = [[1, 2, "NULL"], [3, 4], [5, 6, 7, 8]]
input2 = [[9, 8, "NULL"], [7, 6], [5, 4, 3, 2]]


Then I would like the output to be



output = [[10, 10, "NULL"], [10, 10], [10, 10, 10, 10]]


The inputs will always be nested one level deep, but the outputs ideally should be anything (for instance it could be nested deeper if the function was a "concatenate(a, b)" function)










share|improve this question
















I would like to apply an arbitrary function to two or more nested lists of the same shape. For instance if my function is:



def add(a, b):
if "NULL" not in [a, b]:
return a + b
else:
return "NULL"


and my inputs are:



input1 = [[1, 2, "NULL"], [3, 4], [5, 6, 7, 8]]
input2 = [[9, 8, "NULL"], [7, 6], [5, 4, 3, 2]]


Then I would like the output to be



output = [[10, 10, "NULL"], [10, 10], [10, 10, 10, 10]]


The inputs will always be nested one level deep, but the outputs ideally should be anything (for instance it could be nested deeper if the function was a "concatenate(a, b)" function)







python list






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Mar 28 at 21:30







AAC

















asked Mar 28 at 20:54









AACAAC

2161 silver badge9 bronze badges




2161 silver badge9 bronze badges















  • Will the lists only ever be nested one level deep?

    – Peter Collingridge
    Mar 28 at 21:08











  • @PeterCollingridge Yes, at least in the input stage (perhaps the output could be nested deeper depending on the function applied)

    – AAC
    Mar 28 at 21:24












  • If the lists are nested one level deep aways, why not [func(val) for val in list_of_lists] or event map(func, list_of_lists), it would simplify your function.

    – geckos
    Mar 28 at 21:30

















  • Will the lists only ever be nested one level deep?

    – Peter Collingridge
    Mar 28 at 21:08











  • @PeterCollingridge Yes, at least in the input stage (perhaps the output could be nested deeper depending on the function applied)

    – AAC
    Mar 28 at 21:24












  • If the lists are nested one level deep aways, why not [func(val) for val in list_of_lists] or event map(func, list_of_lists), it would simplify your function.

    – geckos
    Mar 28 at 21:30
















Will the lists only ever be nested one level deep?

– Peter Collingridge
Mar 28 at 21:08





Will the lists only ever be nested one level deep?

– Peter Collingridge
Mar 28 at 21:08













@PeterCollingridge Yes, at least in the input stage (perhaps the output could be nested deeper depending on the function applied)

– AAC
Mar 28 at 21:24






@PeterCollingridge Yes, at least in the input stage (perhaps the output could be nested deeper depending on the function applied)

– AAC
Mar 28 at 21:24














If the lists are nested one level deep aways, why not [func(val) for val in list_of_lists] or event map(func, list_of_lists), it would simplify your function.

– geckos
Mar 28 at 21:30





If the lists are nested one level deep aways, why not [func(val) for val in list_of_lists] or event map(func, list_of_lists), it would simplify your function.

– geckos
Mar 28 at 21:30












2 Answers
2






active

oldest

votes


















2
















How about:



def apply_f(a, b, f):
if isinstance(a, list):
return [apply_f(item_a, item_b, f) for item_a, item_b in zip(a, b)]
else:
return f(a, b)

result = apply_f(input1, input2, add)





share|improve this answer
































    0
















    Assuming the lists are always the right length (you can put a check for this), make your function recursive:



    def add(a, b):

    if isinstance(a, list) and isinstance(b, list):
    for a_sub, b_sub in zip(a, b):
    return [add(a_sub, b_sub) for a_sub, b_sub in zip(a, b)]

    elif "NULL" not in [a, b]:
    return a + b

    elif "NULL" in [a, b]:
    return "NULL"

    else:
    raise ValueError("Wrong input shapes")

    input1 = [[1, 2, "NULL"], [3, 4], [5, 6, 7, 8]]
    input2 = [[9, 8, "NULL"], [7, 6], [5, 4, 3, 2]]

    add(input1, input2)


    Output:



    [[10, 10, 'NULL'], [10, 10], [10, 10, 10, 10]]





    share|improve this answer


























      Your Answer






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      2 Answers
      2






      active

      oldest

      votes








      2 Answers
      2






      active

      oldest

      votes









      active

      oldest

      votes






      active

      oldest

      votes









      2
















      How about:



      def apply_f(a, b, f):
      if isinstance(a, list):
      return [apply_f(item_a, item_b, f) for item_a, item_b in zip(a, b)]
      else:
      return f(a, b)

      result = apply_f(input1, input2, add)





      share|improve this answer





























        2
















        How about:



        def apply_f(a, b, f):
        if isinstance(a, list):
        return [apply_f(item_a, item_b, f) for item_a, item_b in zip(a, b)]
        else:
        return f(a, b)

        result = apply_f(input1, input2, add)





        share|improve this answer



























          2














          2










          2









          How about:



          def apply_f(a, b, f):
          if isinstance(a, list):
          return [apply_f(item_a, item_b, f) for item_a, item_b in zip(a, b)]
          else:
          return f(a, b)

          result = apply_f(input1, input2, add)





          share|improve this answer













          How about:



          def apply_f(a, b, f):
          if isinstance(a, list):
          return [apply_f(item_a, item_b, f) for item_a, item_b in zip(a, b)]
          else:
          return f(a, b)

          result = apply_f(input1, input2, add)






          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Mar 28 at 21:30









          Peter CollingridgePeter Collingridge

          8,5273 gold badges34 silver badges54 bronze badges




          8,5273 gold badges34 silver badges54 bronze badges


























              0
















              Assuming the lists are always the right length (you can put a check for this), make your function recursive:



              def add(a, b):

              if isinstance(a, list) and isinstance(b, list):
              for a_sub, b_sub in zip(a, b):
              return [add(a_sub, b_sub) for a_sub, b_sub in zip(a, b)]

              elif "NULL" not in [a, b]:
              return a + b

              elif "NULL" in [a, b]:
              return "NULL"

              else:
              raise ValueError("Wrong input shapes")

              input1 = [[1, 2, "NULL"], [3, 4], [5, 6, 7, 8]]
              input2 = [[9, 8, "NULL"], [7, 6], [5, 4, 3, 2]]

              add(input1, input2)


              Output:



              [[10, 10, 'NULL'], [10, 10], [10, 10, 10, 10]]





              share|improve this answer





























                0
















                Assuming the lists are always the right length (you can put a check for this), make your function recursive:



                def add(a, b):

                if isinstance(a, list) and isinstance(b, list):
                for a_sub, b_sub in zip(a, b):
                return [add(a_sub, b_sub) for a_sub, b_sub in zip(a, b)]

                elif "NULL" not in [a, b]:
                return a + b

                elif "NULL" in [a, b]:
                return "NULL"

                else:
                raise ValueError("Wrong input shapes")

                input1 = [[1, 2, "NULL"], [3, 4], [5, 6, 7, 8]]
                input2 = [[9, 8, "NULL"], [7, 6], [5, 4, 3, 2]]

                add(input1, input2)


                Output:



                [[10, 10, 'NULL'], [10, 10], [10, 10, 10, 10]]





                share|improve this answer



























                  0














                  0










                  0









                  Assuming the lists are always the right length (you can put a check for this), make your function recursive:



                  def add(a, b):

                  if isinstance(a, list) and isinstance(b, list):
                  for a_sub, b_sub in zip(a, b):
                  return [add(a_sub, b_sub) for a_sub, b_sub in zip(a, b)]

                  elif "NULL" not in [a, b]:
                  return a + b

                  elif "NULL" in [a, b]:
                  return "NULL"

                  else:
                  raise ValueError("Wrong input shapes")

                  input1 = [[1, 2, "NULL"], [3, 4], [5, 6, 7, 8]]
                  input2 = [[9, 8, "NULL"], [7, 6], [5, 4, 3, 2]]

                  add(input1, input2)


                  Output:



                  [[10, 10, 'NULL'], [10, 10], [10, 10, 10, 10]]





                  share|improve this answer













                  Assuming the lists are always the right length (you can put a check for this), make your function recursive:



                  def add(a, b):

                  if isinstance(a, list) and isinstance(b, list):
                  for a_sub, b_sub in zip(a, b):
                  return [add(a_sub, b_sub) for a_sub, b_sub in zip(a, b)]

                  elif "NULL" not in [a, b]:
                  return a + b

                  elif "NULL" in [a, b]:
                  return "NULL"

                  else:
                  raise ValueError("Wrong input shapes")

                  input1 = [[1, 2, "NULL"], [3, 4], [5, 6, 7, 8]]
                  input2 = [[9, 8, "NULL"], [7, 6], [5, 4, 3, 2]]

                  add(input1, input2)


                  Output:



                  [[10, 10, 'NULL'], [10, 10], [10, 10, 10, 10]]






                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered Mar 28 at 21:29









                  dzangdzang

                  6093 silver badges10 bronze badges




                  6093 silver badges10 bronze badges































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