operator.itemgetter() syntax

rogerlew

Hi all,

I need to pass operator.itemgetter(item,...) multiple arguments but the number of arguments is variable.

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ivlist=['var1','var2','var3'] # This variable changes length

keyindices=range(-len(ivlist)-1,0) # = [-4, -3, -2, -1] in this example
 
# What I want in this example is

M_keys=M.keys()

for key in sorted(M_keys,key=operator.itemgetter(-4, -3, -2, -1)):

    # for loop code

What is the syntax for passing operator.itemgetter(items,...) the values of the keyindices list as separate arguments?

Thank you for your help.

rogerlew

I figured it out.

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for key in sorted(M_keys,key=operator.itemgetter(*keyindices)):

ilikepython

I figured it out.

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for key in sorted(M_keys,key=operator.itemgetter(*keyindices)):

Glad you fixed your problem. :)

rogerlew

The method described above works for Python 2.5 but not for 2.4.4. Operator.itemgetter only accepts one argument under 2.4.4. Another problem I found was that with 2.5 the * will only flatten a sequence. So if you want to sort by unordered a set of unordered indices (e.g. -1, 4,5,6) your out of luck (from want I tried at least).

I ended writing a function which works with 2.4 and 2.5. I am posting it here encase someone runs into the same problem and happens to google this in the future.

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def SortKeyByIndices(keylist,indices):

    sortedkeys=sorted(keylist,key=operator.itemgetter(indices[0]))

    if len(indices)>1:

        teeth=[]

        teeth.append([sortedkeys[0][indices[0]],0])

        for ikey, key in enumerate(sortedkeys):

            if key[indices[0]]!=teeth[-1][0]:

                teeth.append([key[indices[0]],ikey])

        teeth.append([teeth[-1][0],len(sortedkeys)])

        for tnum, tooth in enumerate(teeth[:-1]):

            subkeys=sortedkeys[teeth[tnum][1]:teeth[tnum+1][1]]

            subkeys=SortKeyByIndices(subkeys,indices[1:])

            sortedkeys[teeth[tnum][1]:teeth[tnum+1][1]]=subkeys

    return sortedkeys

Usage

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mykeys=mylist.keys()

mykeyssorted=SortKeyByIndices(mykeys,[1,2,5,6])

operator.itemgetter() syntax

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