Python Sort Strings With Digits At The End

October 23, 2024 Post a Comment

what is the easiest way to sort a list of strings with digits at the end where some have 3 digits and some have 4: >>> list = ['asdf123', 'asdf1234', 'asdf111', 'asdf124']

Solution 1:

is there an easy way to do this?

Yes

You can use the natsort module.

>>> from natsort import natsorted
>>> natsorted(['asdf123', 'asdf1234', 'asdf111', 'asdf124'])
['asdf111', 'asdf123', 'asdf124', 'asdf1234']

Full disclosure, I am the package's author.

Solution 2:

is there an easy way to do this?

It's perfectly unclear what the real rules are. The "some have 3 digits and some have 4" isn't really a very precise or complete specification. All your examples show 4 letters in front of the digits. Is this always true?

import re
key_pat = re.compile(r"^(\D+)(\d+)$")
defkey(item):
    m = key_pat.match(item)
    return m.group(1), int(m.group(2))

That key function might do what you want. Or it might be too complex. Or maybe the pattern is really r"^(.*)(\d{3,4})$" or maybe the rules are even more obscure.

>>> data= ['asdf123', 'asdf1234', 'asdf111', 'asdf124']
>>> data.sort( key=key )
>>> data
['asdf111', 'asdf123', 'asdf124', 'asdf1234']

Solution 3:

What you're probably describing is called a Natural Sort, or a Human Sort. If you're using Python, you can borrow from Ned's implementation.

The algorithm for a natural sort is approximately as follows:

Split each value into alphabetical "chunks" and numerical "chunks"
Sort by the first chunk of each value
- If the chunk is alphabetical, sort it as usual
- If the chunk is numerical, sort by the numerical value represented
Take the values that have the same first chunk and sort them by the second chunk
And so on

Solution 4:

l = ['asdf123', 'asdf1234', 'asdf111', 'asdf124']
l.sort(cmp=lambda x,y:cmp(int(x[4:]), int(y[4:]))

Solution 5:

You need a key function. You're willing to specify 3 or 4 digits at the end and I have a feeling that you want them to compare numerically.

sorted(list_, key=lambda s: (s[:-4], int(s[-4:])) if s[-4] in'0123456789'else (s[:-3], int(s[-3:])))

Without the lambda and conditional expression that's

defkey(s):
    if key[-4] in'0123456789':
         return (s[:-4], int(s[-4:]))
    else:
         return (s[:-3], int(s[-3:]))

sorted(list_, key=key)

This just takes advantage of the fact that tuples sort by the first element, then the second. So because the key function is called to get a value to compare, the elements will now be compared like the tuples returned by the key function. For example, 'asdfbad123' will compare to 'asd7890' as ('asdfbad', 123) compares to ('asd', 7890). If the last 3 characters of a string aren't in fact digits, you'll get a ValueError which is perfectly appropriate given the fact that you passed it data that doesn't fit the specs it was designed for.

alezinhacris