New submission from Nico <nico.schloe...@gmail.com>:
Hi,
I ran into a bit of an unexpected issue here with itertools.
I need to say that I discovered itertools only recently, and that maybe my way
of approaching the problem is "not what I want to do". If you think this may be
the case, please let me know.
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.
Is there anything that I can do to debug?
Cheers,
Nico
----------
components: None
files: iterator-test.py
messages: 104917
nosy: nicki
priority: normal
severity: normal
status: open
title: itertools: problem with nested groupby, list()
versions: Python 2.6
Added file: http://bugs.python.org/file17198/iterator-test.py
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue8609>
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