CODEWITHSUNDEEP
pythonsum
ddinchev
ddinchev

Reputation: 34673

How to sum column values with python

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.

Upvotes: 3

Views: 3293

Answers (4)

moldovean
moldovean

Reputation: 3261

Here's another answer, if I may suggest a solution. First put your data in a Matrix. Then, multiply the matrix by a vector of ones. 

import numpy as np
A = np.random.normal(size = (3,3))

Now to get the sum of columns, simply use the dot product.

np.dot(A, np.ones(3))

To stack the rows rather than the columns, simply transpose the matrix.

np.dot(A.T, np.ones(3))

Upvotes: 0

jamylak
jamylak

Reputation: 133554

>>> 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})

Upvotes: 7

Kimvais
Kimvais

Reputation: 39548

Nested generators + list comprehension does the trick:

>>> foo
defaultdict(<type 'dict'>, {u'row1': {u'column1': 33, u'column3': 23, u'column2': 55}, u'row2': {u'column1': 32, u'column3': 17, u'column2': 32}, u'row3': {u'column1': 31, u'column3': 18, u'column2': 87}})
>>> dict(zip(foo.values()[0].keys(), [sum(j[k] for j in (i.values() for _,i in foo.items())) for k in range(3)]))
{u'column1': 96, u'column3': 58, u'column2': 174}

Upvotes: 2

WeaselFox
WeaselFox

Reputation: 7380

not the most pythonic but here:

for val in defaultdict.values() :
   sum1 += val['column1']
   sum2 += val['column2']
   sum3 += val['column3']
final_dict = {'column1' : sum1,'column2' : sum2,'column3' : sum3 }

Upvotes: 0

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