Hi,
I ran into a bit of an unexpected issue here with itertools, and I
need to say that I discovered itertools only recently, so maybe my way
of approaching the problem is "not what I want to do".
Anyway, the problem is the following:
I have a list of dictionaries, something like
[ { "a": 1, "b": 1, "c": 3 },
{ "a": 1, "b": 1, "c": 4 },
...
]
and I'd like to iterate through all items with, e.g., "a":1. What I do
is sort and then groupby,
my_list.sort( key=operator.itemgetter('a') )
my_list_grouped = itertools.groupby( my_list, operator.itemgetter('a') )
and then just very simply iterate over my_list_grouped,
for my_item in my_list_grouped:
# do something with my_item[0], my_item[1]
Now, inside this loop I'd like to again iterate over all items with
the same 'b'-value -- no problem, just do the above inside the loop:
for my_item in my_list_grouped:
# group by keyword "b"
my_list2 = list( my_item[1] )
my_list2.sort( key=operator.itemgetter('b') )
my_list_grouped = itertools.groupby( my_list2,
operator.itemgetter('b') )
for e in my_list_grouped:
# do something with e[0], e[1]
That seems to work all right.
Now, the problem occurs when this all is wrapped into an outer loop, such as
for k in [ 'first pass', 'second pass' ]:
for my_item in my_list_grouped:
# bla, the above
To be able to iterate more than once through my_list_grouped, I have
to convert it into a list first, so outside all loops, I go like
my_list.sort( key=operator.itemgetter('a') )
my_list_grouped = itertools.groupby( my_list, operator.itemgetter('a') )
my_list_grouped = list( my_list_grouped )
This, however, makes it impossible to do the inner sort and
groupby-operation; you just get the very first element, and that's it.
An example file is attached.
Hints, anyone?
Cheers,
Nico
#! /usr/bin/env python
# -*- coding: utf-8 -*-
import operator, itertools
my_list = [ { "a": 1, "b": 1, "c": 3 },
{ "a": 1, "b": 1, "c": 4 },
{ "a": 1, "b": 11, "c": 3 },
{ "a": 1, "b": 11, "c": 4 },
{ "a": 2, "b": 1, "c": 3 },
{ "a": 2, "b": 1, "c": 4 },
{ "a": 2, "b": 11, "c": 3 },
{ "a": 2, "b": 11, "c": 4 } ]
# group my_list by "a"
my_list.sort( key=operator.itemgetter('a') )
my_list_grouped = itertools.groupby( my_list, operator.itemgetter('a') )
my_list_grouped = list( my_list_grouped )
for k in [ 'first pass', 'second pass' ]:
print k
for my_item in my_list_grouped:
print "\t" + str( my_item[0] )
# group by keyword "b"; need to get list first to be able to use 'sort'
my_list2 = list( my_item[1] )
my_list2.sort( key=operator.itemgetter('b') )
my_list_grouped = itertools.groupby( my_list2, operator.itemgetter('b') )
for e in my_list_grouped:
print "\t\t" + str( e[0] )
lll = list( e[1] )
for ee in lll:
print "\t\t\t" + str( ee )--
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