Consider adding a `zipdict()` function

[ankostis]

Please consider adding a zipdict() function that mimics the zip() function but on dictionaries This utility allows to iterate the items (key,value) of a list of dictionaries based on their common keys.

The necessity for such a function is described in this SO question: http://stackoverflow.com/questions/16458340/python-equivalent-of-zip-for-dictionaries

A starting implementation would be based on @Volatilty's suggestion in the above question:

def zipdict(*dcts):
    if dcts:
        for k in set(dcts[0]).intersection(*dcts[1:]):
            yield k, tuple(d[k] for d in dcts)

[eriknw]

Interesting suggestion. If you knew the keys in the dict are identical, one could simply do:

>>> import toolz
>>> da = {'a': 1, 'b': 2, 'c': 3}
>>> db = {'a': 4, 'b': 5, 'c': 6}
>>> toolz.merge_with(tuple, da, db)
{'a': (1, 4), 'c': (3, 6), 'b': (2, 5)}

If the keys aren't identical, then the operation seems weird to me. Should you only include the intersection of keys, use a default for missing values, or make this an option? Should this be left for the user to spell out explicitly using keyfilter on the inputs or valfilter on the output?

My inclination would be to have zipdict return a dict if it's added to dicttoolz, not a generator of items. Thoughts?

[ankostis]

If the keys aren't identical, then the operation seems weird to me.

Typically the keys partly overlap; but actually it shouldn't matter.
I had crafted some elaborate performance code to check for various contention cases, if you are interested.

Should you only include the intersection of keys, use a default for missing values, or make this an option?

zip() iterates just on the shortest list (so "intersection" it is) - why should zipdict() support otherwise?

My inclination would be to have zipdict return a dict if it's added to dicttoolz, not a generator of items. Thoughts?

I had also given thought on that.
I would follow the zip() contract again, and return a generator - so it should be added, counter-intuitively I musts say, into the itertoolz :-)

[ankostis]

Any progress on that?

[ankostis]

ping??

[groutr]

This is interesting.