Sorting a multidimensional array by multiple keys

[Steven Bethard]

Rehceb Rotkiv wrote:
>> If you want a good answer you have to give me/us more details, and an
>> example too.
> 
> OK, here is some example data:
> 
> reaction is BUT by the
> sodium , BUT it is
> sea , BUT it is
> this manner BUT the dissolved
> pattern , BUT it is
> rapid , BUT it is
> 
> As each line consists of 5 words, I would break up the data into an array 
> of five-field-arrays (Would you use lists or tuples or a combination in 
> Python?). The word "BUT" would be in the middle, with two fields/words 
> left and two fields/words right of it. I then want to sort this list by
> 
> - field 3
> - field 4
> - field 1
> - field 0

You're probably looking for the key= argument to list.sort().  If your 
function simply returns the fields in the order above, I believe you get 
the right thing::

 >>> s = '''\
... reaction is BUT by the
... sodium , BUT it is
... sea , BUT it is
... this manner BUT the dissolved
... pattern , BUT it is
... rapid , BUT it is
... '''
 >>> word_lists = [line.split() for line in s.splitlines()]
 >>> def key(word_list):
...     return word_list[3], word_list[4], word_list[1], word_list[0]
...
 >>> word_lists.sort(key=key)
 >>> word_lists
[['reaction', 'is', 'BUT', 'by', 'the'],
  ['pattern', ',', 'BUT', 'it', 'is'],
  ['rapid', ',', 'BUT', 'it', 'is'],
  ['sea', ',', 'BUT', 'it', 'is'],
  ['sodium', ',', 'BUT', 'it', 'is'],
  ['this', 'manner', 'BUT', 'the', 'dissolved']]

STeVe