Question

I have a rowset that looks like this:

defaultdict(<type 'dict'>, 
{
   u'row1': {u'column1': 33, u'column2': 55, u'column3': 23}, 
   u'row2': {u'column1': 32, u'column2': 32, u'column3': 17}, 
   u'row3': {u'column1': 31, u'column2': 87, u'column3': 18}
})

I want to be able to easily get the sum of column1, column2, column3. It would be great if I could do this for any number of columns, receiving the result in a hash map that looks like columnName => columnSum. As you might guess, its not possible for me to obtain the summed values from the database in first place, thus the reason to ask the question.

Answer 1

>>> from collections import defaultdict
>>> x = defaultdict(dict, 
    {
        u'row1': {u'column1': 33, u'column2': 55, u'column3': 23}, 
        u'row2': {u'column1': 32, u'column2': 32, u'column3': 17}, 
        u'row3': {u'column1': 31, u'column2': 87, u'column3': 18}
    }) 

>>> sums = defaultdict(int)
>>> for row in x.itervalues():
        for column, val in row.iteritems():
            sums[column] += val


>>> sums
defaultdict(<type 'int'>, {u'column1': 96, u'column3': 58, u'column2': 174})

Ooh a much better way!

>>> from collections import Counter
>>> sums = Counter()
>>> for row in x.values():
        sums.update(row)


>>> sums
Counter({u'column2': 174, u'column1': 96, u'column3': 58})