I have a dictionary. The keys are dates (datetime). I need to sort the dictionary so that the values in the dictionary are sorted by date - so that by iterating through the dictionary, I am processing items in the desired chronological (i.e. date/time) order.
How may I sort such a dictionary by date?
Example:
mydict = { '2000-01-01': {fld_1: 1, fld_2: 42}, '2000-01-02': {fld_1:23, fld_2: 22.17} }
Note: I am using strings here instead of datetime, to keep the example simple
If you're using Python 2.7+ or 3.1+ you could create an OrderedDict from collections from a sort of your dictionary and then iterate through that.
from collections import OrderedDict
ordered = OrderedDict(sorted(mydict.items(), key=lambda t: t[0]))
However, depending on what you want to do it's probably easier to iterate over a sorted list of keys from your dict.
OrderedDict or retrieving and then sorting the keys after any changes are made to the dictionary, would be a SortedDict.
key when they just want the natural sort order?
ordered = OrderedDict(sorted(mydict.items()) Note that the sort works the same if the keys are actual datetime objects and not stringssorteddict extension module instead of what's in this answer (or the alternative in your comment). "The main benefit of sorteddicts is that you never have to explicitly sort."Dictionaries are unsortable. Iterate over sorted(mydict.keys()) instead.
sorted(mydict) if you prefer.Dictionaries never store anything in some order. But you can get a list of keys using d.keys() which could be sorted. Iterate over a generator like below.
def sortdict(d):
for key in sorted(d): yield d[key]
Using this you will be able to iterate over values in chronological order.
for value in sortdict(mydict):
# your code
pass
.keys() there
since your date strings seem to be in a proper format you could just do:
>>> sorted(mydict.items()) # iteritems in py2k
[('2000-01-01', {'fld_2': 42, 'fld_1': 1}), ('2000-01-02', {'fld_2': 22.17, 'fld_1': 23})]
I'm sure that python knows how to compare dates. So:
def sortedDictValues(adict):
items = adict.items()
items.sort()
return [value for key, value in items]
datetime objects without any problems. In this case YYYY-MM-DD strings are also correctly comparable. A problem would be date in format MM/DD/YYYY or DD.MM.YYYY, but not with YYYY-MM-DD.return [value for key, value in sorted(adict.items())]Python 2.7 (released on July 3rd, 2010) supports an ordered dictionary type:
