CODEWITHSUNDEEP
pythonlistpython-2.7sorting
Pigna
Pigna

Reputation: 2924

How to sort list of strings by count of a certain character?

I have a list of strings and I need to order it by the appearance of a certain character, let's say "+". So, for instance, if I have a list like this: 

["blah+blah", "blah+++blah", "blah+bl+blah", "blah"]

I need to get:

["blah", "blah+blah", "blah+bl+blah", "blah+++blah"]

I've been studying the sort() method, but I don't fully understand how to use the key parameter for complex order criteria. Obviously sort(key=count("+")) doesn't work. Is it possible to order the list like I want with sort() or do I need to make a function for it?

Upvotes: 6

Views: 4366

Answers (2)

vaultah
vaultah

Reputation: 46533

Yes, list.sort can do it, though you need to specify the key argument:

In [4]: l.sort(key=lambda x: x.count('+'))

In [5]: l
Out[5]: ['blah', 'blah+blah', 'blah+bl+blah', 'blah+++blah']

In this code key function accepts a single argument and uses str.count to count the occurrences of '+' in it.

As for list.sort(key=count('+')), you can get it to work if you define the count function like this (with operator.methodcaller):

count = lambda x: methodcaller('count', x) # from operator import methodcaller

Upvotes: 14

Anand S Kumar
Anand S Kumar

Reputation: 90899

You can use -

s = ["blah+blah","blah+++blah","blah+bl+blah","blah"]
print(sorted(s,key=lambda t: t.count('+')))
>>["blah","blah+blah","blah+bl+blah","blah+++blah"]

Upvotes: 0

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