Question

Using Python NumPy to calculate the sum of the column of a matrix:

import numpy
from StringIO import StringIO

fileName = 'test2.csv'
myFile = open(fileName,'r')
print "Reading data from '%s' ..." % fileName
data = myFile.read() 
myFile.close()

data = numpy.genfromtxt(StringIO(data), delimiter=',', usecols=(0,1,2))
print "Calculating ..."

print data[:,2]
sumA1 = data[:,2].sum
print "shape =", data.shape
print "sumA1 =", str(sumA1)
print "ok"

Then contents of test2.csv:

12,13,14,17
1,2,3,4
12,13,14,17
1,2,3,4
12,13,14,17
1,2,3,4
12,13,14,17
1,2,3,4
12,13,14,17

I get this output

Reading data from 'test2.csv' ...
Calculating ...
[ 14.   3.  14.   3.  14.   3.  14.   3.  14.]
shape = (9, 3)
sumA1 = <built-in method sum of numpy.ndarray object at 0x00FD8EF8>
ok

Why can’t I get “sumA1 = 82” insted of that weird message? What am I doing wrong?

Thank you very much in advance.

Answer 1

You have to make a call of the sum function. Just replace this piece of code:

sumA1 = data[:,2].sum

with this one:

sumA1 = data[:,2].sum()