Python intersection of datetimes from multiple lists/dictionaries

Question

I have a variable named records that looks like this:

records = {
    'set1': [{'Time Stamp': datetime, 'data': data, ...}, {'Time Stamp': datetime, 'data': data, ...}, ...],
    'set2': [{'Time Stamp': datetime, 'data': data, ...}, {'Time Stamp': datetime, 'data': data, ...}, ...]
    .
    .
    .
}

I'm trying to delete all the dictionaries (the ones with 'Time Stamp' in it) that don't have common time stamps amongst the other 'sets'.

My first thought was to create a variable from records that would look like this:

var = {
    'set1': [datetime, datetime, ...],
    'set2': [datetime, datetime, ...],
    .
    .
    .
}

And from there loop through something like list(set(a) & set(b)) (from here) to get a list of all the common time stamps.

How could I create the variable var? I assume it can be done with a list generator expression, I just don't know how to create them.

And if you don't think this is the right approach, how would you do it? In terms of time complexity, there won't ever be anymore than 10 'sets', but each set has around 4,000 dictionaries each with about 5 keys/values in them.

Edit: To simplify the question, how can you create a list from a list of dictionaries? To illustrate this:

dict = {'time': timevalue, 'otherstuff': othervalue}
list = [dict, dict, dict] # a list of dictionaries in the form of dict
# create result
result = [timevalue, timevalue, timevalue, timevalue]

I think you have a typo in your code. Oh wait, there is no code! — planestepper, Aug 19 '14 at 17:47
Please include sample input, expected output, the code you have tried (however trivial it might be) — shaktimaan, Aug 19 '14 at 17:52

score 0 · Answer 1 · answered Aug 19 '14 at 18:14

>>> import datetime
>>> 
>>> my_dict = {'time': datetime.datetime.now(), 'otherstuff': 'fooo'}
>>> my_list = [my_dict for i in xrange(3)]
>>> result = [d['time'] for d in my_list]
>>> result
[datetime.datetime(2014, 8, 19, 14, 13, 3, 620886), datetime.datetime(2014, 8, 19, 14, 13, 3, 620886), datetime.datetime(2014, 8, 19, 14, 13, 3, 620886)]
>>>

score -2 · Accepted Answer · answered Aug 19 '14 at 18:08

-2

Something like this maybe:

var = {}
for set, list in records.iteritems():
    var[set] = [i['Time Stamp'] for i in list]

answered Aug 19 '14 at 18:08

Mike

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Python intersection of datetimes from multiple lists/dictionaries

2 Answers2