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Revolucion for Monica
Asked: 2020-04-29 06:05:57 +0800 CST 2020-04-29 06:05:57 +0800 CST

get the minimum index of a List in a program

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I have a problem in Python. I want to get the minimum index of a List:

for j in range(nbr_usines):
    L.append(Dij[j][i])
indice_min=L.index(min(L))

In the terminal it is fine with L.index(min(L)), but when I compile the program programa(Bij,Dij,Vi,Pi)it tells me:

ValueError: min() arg is an empty sequence
python

1 Answers

  1. Best Answer

    The error occurs because you are applying min()to an empty list . You can reproduce it with:

    L=[]
indice_min=L.index(min(L))

    For some reason Lit is an empty list, possibly, given what you show, it is because it is equal to nbr_usines0). If this should not happen, check your code because you are generating the list wrong. Instead, if this possibility exists naturally in your program, then you should handle the exception. One solution would be to use a conditional that checks whether or not the list is empty:

    if L:
    indice_min = L.index(min(L))
else:
    indice_min = None

    Or more compactly:

    indice_min = L.index(min(L)) if L else None

    Or use try-except:

    for j in range(nbr_usines):
    L.append(Dij[j][i])

try:
    indice_min = L.index(min(L))
except ValueError:
    indice_min = None

    If you also need the element itself in addition to its index, you have other possibilities:

    • Use a generator and enumerate:

      if L:
    valor, indice = min((v,i) for i,v in enumerate(L))
else:
    valor, indice = None, None

      The same in one line:

      valor, indice = min((v,i) for i,v in enumerate(L)) if L else (None, None)

    • Use operator.itemgettertogether with enumerate:

      import operator

if L:
    indice, valor = min(enumerate(L), key=operator.itemgetter(1))
else:
    indice, valor = None, None

      or alternatively:

      import operator

indice, valor = min(enumerate(L), key=operator.itemgetter(1)) if L else (None, None)

    In all cases if the list is empty it is returned None, you can modify this as you like depending on what you use it for in your entire program.

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