CODEWITHSUNDEEP
pythonlistsortingzip
rectangletangle
rectangletangle

Reputation: 53051

How do I sort a zipped list in Python?

What's the Pythonic way to sort a zipped list?

code :

names = list('datx')
vals  = reversed(list(xrange(len(names))))
zipped = zip(names, vals)

print zipped

The code above prints [('d', 3), ('a', 2), ('t', 1), ('x', 0)]

I want to sort zipped by the values. So ideally it would end up looking like this [('x', 0), ('t', 1), ('a', 2), ('d', 3)].

Upvotes: 54

Views: 80066

Answers (6)

Max Kleiner
Max Kleiner

Reputation: 1622

Sort feature importance in a classifier (dtc=decision_tree):

for name, importance in sorted(zip(X_train.columns, 
                dtc.feature_importances_),key=lambda x: x[1]):
    print(name, importance)

Upvotes: 0

Owen
Owen

Reputation: 39366

sorted(zipped, key = lambda t: t[1])

Upvotes: 50

MSeifert
MSeifert

Reputation: 152870

In your case you don't need to sort at all because you just want an enumerated reversed list of your names:

>>> list(enumerate(names[::-1]))      # reverse by slicing
[(0, 'x'), (1, 't'), (2, 'a'), (3, 'd')]

>>> list(enumerate(reversed(names)))  # but reversed is also possible
[(0, 'x'), (1, 't'), (2, 'a'), (3, 'd')]

But if you need to sort it then you should use sorted (as provided by @utdemir or @Ulrich Dangel) because it will work on Python2 (zip and itertools.zip) and Python3 (zip) and won't fail with an AttributeError like .sort(...) (which only works on Python2 zip because there zip returns a list):

>>> # Fails with Python 3's zip:
>>> zipped = zip(names, vals)
>>> zipped.sort(lambda x: x[1])
AttributeError: 'zip' object has no attribute 'sort'

>>> # Fails with Python 2's itertools izip:
>>> from itertools import izip
>>> zipped = izip(names, vals)
>>> zipped.sort(lambda x: x[1])
AttributeError: 'itertools.izip' object has no attribute 'sort'

But sorted does work in each case:

>>> zipped = izip(names, vals)
>>> sorted(zipped, key=lambda x: x[1])
[('x', 0), ('t', 1), ('a', 2), ('d', 3)]

>>> zipped = zip(names, vals)  # python 3
>>> sorted(zipped, key=lambda x: x[1])
[('x', 0), ('t', 1), ('a', 2), ('d', 3)]

Upvotes: 5

Zach Kelling
Zach Kelling

Reputation: 53879

It's simpler and more efficient to zip them in order in the first place (if you can). Given your example it's pretty easy:

>>> names = 'datx'
>>> zip(reversed(names), xrange(len(names)))
<<< [('x', 0), ('t', 1), ('a', 2), ('d', 3)]

Upvotes: 4

utdemir
utdemir

Reputation: 27266

import operator
sorted(zipped, key=operator.itemgetter(1))

If you want it a little bit more faster, do ig = operator.itemgetter(1) and use ig as key function.

Upvotes: 10

Ulrich Dangel
Ulrich Dangel

Reputation: 4625

Quite simple:

sorted(zipped, key=lambda x: x[1])

Upvotes: 85

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