Question

I am fairly new to dictionaries, so this is probably a fairly basic question.

Let’s say I have two different dictionaries with similar elements.
Example:

    Dictionary1 = {'Bob' : 1, 'Mary' : 2, 'Sue' : 3, 'George' : 4}
    Dictionary2 = {'Bob' : 1, 'Sue' : 2, 'Jill' : 3, 'Isaac' : 4, 'George' : 5}

I want to be able to take the intersection of the two dictionaries and apply the indices of the first dictionary to the second. So I want an output that looks something like this:

    DictionaryCombo = {'Bob' : 1, 'Sue' : 3, 'George' : 4}

Please excuse my formatting for my desired output, as I am not certain what it should look like, though I know that I want the key and value pairs of the intersection of the two dictionaries.

Answer 1

If you want to subset d1 so it only has elements present in d2

d1 = {'Bob': 1, 'Mary': 2, 'Sue': 3, 'George': 4}
d2 = {'Bob': 101, 'Sue': 102, 'Jill': 103, 'Isaac': 104, 'George': 105}
{k: v for k, v in d1.items() if k in d2}
# {'Bob': 1, 'Sue': 3, 'George': 4}

Or you mention apply, so did you want to update values in d2?

d2.update(d1)
print d2
# {'Sue': 3, 'Mary': 2, 'Jill': 103, 'Isaac': 104, 'Bob': 1, 'George': 4}

Or, if you really are starting with two lists (and not starting with dict’s):

el1 = ['Bob', 'Mary', 'Sue', 'George']
el2 = ['Bob', 'Sue', 'Jill', 'Isaac', 'George']
dict( (val, idx) for idx, val in enumerate(d1, start=1) if val in set(el2) )
#{'Bob': 1, 'Sue': 3, 'George': 4}

If you have two lists, one of keys, and one of values, and wish to make them a dict, then you can use zip:

keys = ['Bob', 'Mary', 'Sue', 'George']  
vals = [1, 2, 3, 4]
dict( zip(keys, vals) )
# {'Bob': 1, 'Mary': 2, 'Sue': 3, 'George': 4}