Python Line Sorting -

Question

I have the following:

line  = ['aaaa, 1111, BOB, 7777','aaaa, 1111, BOB, 8888','aaaa, 1111, larry, 7777',,'aaaa, 1111, Steve, 8888','BBBB, 2222, BOB, 7777']

Is there away I can sort by (Bob,Larry,Steve) then by (1111,2222)?

so...

for i in line:
    i = i.split(' ')
    pos1 = i[0]
    pos2 = i[1]
    pos3 = i[2]
    pos4 = i[3]

So I need to sort by pos3 and then by pos2.

Desired output would be:

'aaaa, 1111, BOB, 7777'
'aaaa, 1111, BOB, 8888'
'BBBB, 2222, BOB, 7777'
'aaaa, 1111, larry, 7777'
'aaaa, 1111, Steve, 8888'

Martijn Pieters · Accepted Answer · 2014-01-22 18:06:06Z

6

Leave the splitting to a key function:

sorted(line, key=lambda l: l.lower().split(', ')[2:0:-1])

This returns the strings in line in lexicographically sorted order, case-insensitive. The [2:0:-1] slice returns the third and second columns in reverse order.

Demo:

>>> line  = ['aaaa, 1111, BOB, 7777','aaaa, 1111, BOB, 8888','aaaa, 1111, larry, 7777','aaaa, 1111, Steve, 8888','BBBB, 2222, BOB, 7777']
>>> from pprint import pprint
>>> pprint(sorted(line, key=lambda l: l.lower().split(', ')[2:0:-1]))
['aaaa, 1111, BOB, 7777',
 'aaaa, 1111, BOB, 8888',
 'BBBB, 2222, BOB, 7777',
 'aaaa, 1111, larry, 7777',
 'aaaa, 1111, Steve, 8888']

If your 'lines' are not as neatly comma + space separated, you may need to strip whitespace too.

edited Jan 22, 2014 at 18:06

answered Jan 22, 2014 at 17:55

Martijn Pieters

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4 Comments

Trying_hard Over a year ago

That doesn't seem to give me the desired output I added above

Martijn Pieters Over a year ago

@Dumbkid_trying: Made it case-insensitive, fixed the incorrect slice (I missed how you numbered your columns).

Trying_hard Over a year ago

perfect, how is this )[2:0:-1])) splitting it. Just trying to get a better understanding

Martijn Pieters Over a year ago

@Dumbkid_trying: It is not. .split(', ') does the splitting, returning a list. The [2:0:-1] takes a slice from that list, in reverse order (the last element :-1 defines the stride, negative strides count backwards). It starts at index 2, then counts down to index 0 (which is not included). So in the end a new list is returned containing index 2 and index 1, in that order.

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