Python sorting a list of strings

Question

How would I sort this?

>>> list = ["a_0","a_1","a_2","a_3","a_10","a_11","a_23","a_5","a_6","a_5"]
>>> sorted(list)
['a_0', 'a_1', 'a_10', 'a_11', 'a_2', 'a_23', 'a_3', 'a_5', 'a_5', 'a_6']>

What I need it to be is:

['a_0', 'a_1', 'a_2', 'a_3', 'a_5', 'a_5', 'a_6, 'a_10', 'a_11', 'a_23']>

So it's sorted based on the "number".

taijirobot2 · Accepted Answer · 2011-06-01 09:20:45Z

10

do you mean this: sorted(list, key=lambda d: int(d[2:])) ?

answered Jun 1, 2011 at 9:20

taijirobot2

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2 Comments

Thomas Wouters Over a year ago

Note that this will sort only based on the number, and not on the 'a' at all. It also requires that the digits start at character 2.

taijirobot2 Over a year ago

"Note that this will sort only based on the number", indeed

Thomas Wouters · Accepted Answer · 2011-06-01 09:24:17Z

6

You need to write a "key function" that translates your string into a search key that has the ordering you want. For example:

def key(k):
    s, sep, i = k.partition('_')
    return (s, int(i))

>>> L = ["a_0","a_1","b_2","c_2","a_10","a_11","a_23","b_5","a_6","c_5"]
>>> sorted(L, key=key)
['a_0', 'a_1', 'a_6', 'a_10', 'a_11', 'a_23', 'b_2', 'b_5', 'c_2', 'c_5']

answered Jun 1, 2011 at 9:24

Thomas Wouters

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1 Comment

Harry Over a year ago

thanks, this is actually what I needed for my exact purpose. I changed it a bit, now works perfect. Although your answer is correct, I have marked the answer above correct based on the question.

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