Python Collections Counter for a List of Dictionaries

Question

I have a dynamically growing list of arrays that I would like to add like values together. Here\'s an example:

{\"something\" : [{\"one\":\"200\"}, {\"three\         


        

Answer 1

I think this does what you want, but I'm not sure because I don't know what "The dict is also being dynamically created, so I can't build the list without the dicts" means. Still:

input = {
    "something" : [{"one":"200"}, {"three":"400"}, {"one":"100"}, {"two":"800"}], 
    "foo" : [{"a" : 100, "b" : 200}, {"a" : 300, "b": 400}],
}

def counterize(x):
    return Counter({k : int(v) for k, v in x.iteritems()})

counts = {
    k : sum((counterize(x) for x in v), Counter()) 
    for k, v in input.iteritems()
}

Result:

{
    'foo': Counter({'b': 600, 'a': 400}), 
    'something': Counter({'two': 800, 'three': 400, 'one': 300})
}

I expect using sum with Counter is inefficient (in the same way that using sum with strings is so inefficient that Guido banned it), but I might be wrong. Anyway, if you have performance problems, you could write a function that creates a Counter and repeatedly calls += or update on it:

def makeints(x):
    return {k : int(v) for k, v in x.iteritems()}

def total(seq):
    result = Counter()
    for s in seq:
        result.update(s)
    return result

counts = {k : total(makeints(x) for x in v) for k, v in input.iteritems()}