[Tutor] List processing question - consolidating duplicate entries

[Richard Querin]

On Nov 27, 2007 5:40 PM, Kent Johnson <kent37 at tds.net> wrote:

>
> This is a two-liner using itertools.groupby() and operator.itemgetter:
>
> data = [['Bob', '07129', 'projectA', '4001',5],
> ['Bob', '07129', 'projectA', '5001',2],
> ['Bob', '07101', 'projectB', '4001',1],
> ['Bob', '07140', 'projectC', '3001',3],
> ['Bob', '07099', 'projectD', '3001',2],
> ['Bob', '07129', 'projectA', '4001',4],
> ['Bob', '07099', 'projectD', '4001',3],
> ['Bob', '07129', 'projectA', '4001',2]
> ]
>
> import itertools, operator
> for k, g in itertools.groupby(sorted(data), key=operator.itemgetter(0,
> 1, 2, 3)):
>   print k, sum(item[4] for item in g)
>


I'm trying to understand what's going on in the for statement but I'm having
troubles. The interpreter is telling me that itemgetter expects 1 argument
and is getting 4.

I understand that groupby takes 2 parameters the first being the sorted
list. The second is a key and this is where I'm confused. The itemgetter
function is going to return a tuple of functions (f[0],f[1],f[2],f[3]).

Should I only be calling itemgetter with whatever element (0 to 3) that I
want to group the items by?

I'm almost getting this but not quite. ;)

RQ
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