Python array sorting

Question

I want to sort a list so that I can feed in an attribute of the list into a loop. Let me elaborate :

Let's say I have:

data = [('turtle', 'sock'), ('frog', 'hat'), ('turtle', 'shirt'), ('frog', 'boot')]

and I only want the tuples that are related to the 'turtle', so I want:

newdata = [('turtle', 'sock'), ('turtle', 'shirt')]

Then I want to put 'sock' and 'shirt' in a list so that I can do something like:

lst = ['sock', 'shirt']

Then I can do something like

print "what is the turtle wearing?" 
for item in lst:
    print "the turtle is wearing a " + item

My idea was to sort the array so that all things related to the turtle could be put into a separate list. Then split that, but my knowledge of list is minimal. So any help or forwarding to helpful links is greatly appreciated. I hope this is a nice basic example to express my needs.

I will be presented with data in an array. If using your suggestion is easier I would love to hear how to use that instead. — Plato's Student
– Plato's Student, Commented Jun 6, 2014 at 16:18
sorted(list(map(operator.itemgetter(1), filter(lambda x: x[0] == 'turtle', data)))). Oh yeah, don't forget to import operator — khachik
– khachik, Commented Jun 6, 2014 at 16:19
... but it is better to process the list once and generate a dict item -> wearing dict as @FatalError suggested. — khachik
– khachik, Commented Jun 6, 2014 at 16:21
Okay I looked them up some, I think that may work well! do you know of a good place for examples? — Plato's Student
– Plato's Student, Commented Jun 6, 2014 at 16:23

FatalError · Accepted Answer · 2014-06-06 16:23:49Z

6

It's probably most appropriate to build a dict that holds what each animal wears (as I mentioned in the comment):

from collections import defaultdict

data = [('turtle', 'sock'), ('frog', 'hat'), ('turtle', 'shirt'), ('frog', 'boot')]

d = defaultdict(list)
for animal, clothing in data:
    d[animal].append(clothing)

print d['turtle']

answered Jun 6, 2014 at 16:23

FatalError

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DeeTee · Accepted Answer · 2014-06-06 16:26:14Z

0

data = [('turtle', 'sock'), ('frog', 'hat'), ('turtle', 'shirt'), ('frog', 'boot')]

def function(key):
    listWithKey = []
    for element in data:
        if element[0] == key:
            listWithKey.append(element[1])
    return listWithKey

print(function("turtle"))

This is a more basic approach just using lists and loops. The output is ['sock', 'shirt']

answered Jun 6, 2014 at 16:26

DeeTee

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1 Comment

Ralf Haring Over a year ago

This approach could be written more simply using list comprehensions. [x[1] for x in data if x[0] == 'turtle']

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