Pythonic list reordering
Ben Racine
['dir_0_error.dat', 'dir_120_error.dat', 'dir_30_error.dat', 'dir_330_error.dat']
I want to sort it based upon the numerical value only.
Does someone have an elegant solution to this?
Thanks,
Ben R.
Chris Rebert
> I have a list...
>
> ['dir_0_error.dat', 'dir_120_error.dat', 'dir_30_error.dat', 'dir_330_error.dat']
>
> I want to sort it based upon the numerical value only.
a = ['dir_0_error.dat', 'dir_120_error.dat', 'dir_30_error.dat',
'dir_330_error.dat']
def key(item):
return int(item.split('_')[1])
a.sort(key=key)
Cheers,
Chris
--
http://blog.rebertia.com
Gary Herron
> I have a list...
>
> ['dir_0_error.dat', 'dir_120_error.dat', 'dir_30_error.dat', 'dir_330_error.dat']
>
> I want to sort it based upon the numerical value only.
>
>
> Thanks,
> Ben R.
>
How about a one liner?
L.sort(key=lambda s: int(s.split('_')[1]))
(Which is not necessarily elegant, but it is short.)
Gary Herron
Joaquin Abian
not sure about elegance, but my two cents:
>> mylist = ['dir_0_error.dat', 'dir_120_error.dat', 'dir_30_error.dat', 'dir_330_error.dat']
>> mylist = [(int(item.split('_')[1]), item) for item in mylist]
>> mylist.sort()
>> mylist = [item for idx, item in mylist]
>> mylist
['dir_0_error.dat', 'dir_30_error.dat', 'dir_120_error.dat',
'dir_330_error.dat']
joaquin
Lie Ryan
list.sort() and sorted() accept `key` argument, which receives a
callable that transform the item to be sorted into sorting key. So if
you have:
l = ['dir_30_error.dat', 'dir_120_error.dat',
'dir_330_error.dat', 'dir_0_error.dat']
# 'dir_0_error.dat' -> 0
# 'dir_30_error.dat' -> 30
def getnum(s):
return int(''.join(x for x in s if x.isdigit()))
# sort based on getnum()'s return value
l.sort(key=getnum)
Chris Rebert
> On Apr 9, 12:52 am, Ben Racine <i3enha...@gmail.com> wrote:
>> I have a list...
>>
>> ['dir_0_error.dat', 'dir_120_error.dat', 'dir_30_error.dat', 'dir_330_error.dat']
>>
>> I want to sort it based upon the numerical value only.
>>
>> Does someone have an elegant solution to this?
>
>
>>> mylist = ['dir_0_error.dat', 'dir_120_error.dat', 'dir_30_error.dat', 'dir_330_error.dat']
>>> mylist = [(int(item.split('_')[1]), item) for item in mylist]
>>> mylist.sort()
>>> mylist = [item for idx, item in mylist]
>>> mylist
>
> ['dir_0_error.dat', 'dir_30_error.dat', 'dir_120_error.dat',
> 'dir_330_error.dat']
At least conceptually, that's how list.sort() with a key= argument
works internally (i.e. via Schwartzian transform).
Joaquin Abian
Chris, thanks for the comment. I did not know that name (Schwartzian
transform)
I knew it as the decorate-sort-undecorate strategy.
Now after learning that it was a Perl idiom I feel somewhat
embarrassed ;-)
BTW, I actually prefer the l.sort(key=f) method.
Just my lazy neurons were back to Python 2.3 when I wrote the
response.
Joaquin
Tobiah
> How about a one liner?
>
> L.sort(key=lambda s: int(s.split('_')[1]))
>
> (Which is not necessarily elegant, but it is short.)
I grant it a measure of elegance as well.
Kent Engström
> I have a list...
>
> ['dir_0_error.dat', 'dir_120_error.dat', 'dir_30_error.dat', 'dir_330_error.dat']
>
> I want to sort it based upon the numerical value only.
>
> Does someone have an elegant solution to this?
I use code like the hack below to sort miscellaneous strings that
consist of mixed numerical and non-numerical parts.
import re
nsk_re = re.compile("([0-9]+)|([^0-9]+)")
def numeric_sort_key(x):
return [handle_int_nonint(i_ni) for i_ni in nsk_re.findall(x)]
def handle_int_nonint(int_nonint_tuple):
if int_nonint_tuple[0]:
return int(int_nonint_tuple[0])
else:
return int_nonint_tuple[1]
def numerically_sorted(l):
return sorted(l, key=numeric_sort_key)
alex23
This approach doesn't rely on knowing the format of the string:
>>> from string import maketrans, letters, punctuation
>>> a = ['dir_0_error.dat', 'dir_120_error.dat', 'dir_30_error.dat', 'dir_330_error.dat']
>>> def only_numbers(s):
... nums = s.translate(None, letters+punctuation)
... return int(nums)
...
>>> a.sort(key=only_numbers)
>>> a
['dir_0_error.dat', 'dir_30_error.dat', 'dir_120_error.dat',
'dir_330_error.dat']
If you're using Python 3.x, the string module has been removed, so you
can find the maketrans function on str there.
MRAB
The string module still exists in Python 3.x, but the string functions
which have been superseded by string methods have been removed.
alex23
> The string module still exists in Python 3.x, but the string functions
> which have been superseded by string methods have been removed.
Awesome, thanks for the heads up.