Sum elements in a row (Python/Numpy)

Question

Working on a project that gives us free reign on what to use. So I decided I'd learn python for it.

To make this short, I want sum all the elements in a "row" of a matrix I'm reading in.

This is what my 2D array looks like after I read in my table from my text file.

['0000' '0' '0' '0' '0' '0' '0' '0' '0' '0' '0' '0' '0' '0' '1']
['0001' '0' '1' '0' '1' '0' '0' '0' '0' '1' '0' '0' '0' '0' '1']
['0010' '0' '1' '0' '1' '0' '0' '0' '0' '1' '0' '0' '0' '0' '1']
['0011' '0' '1' '0' '1' '0' '0' '0' '0' '1' '0' '0' '0' '0' '1']
['0100' '0' '0' '0' '0' '0' '1' '0' '1' '0' '0' '1' '0' '0' '1']
['0101' '0' '0' '1' '0' '0' '0' '1' '0' '0' '1' '0' '1' '1' '0']
['0110' '0' '0' '1' '0' '1' '0' '0' '0' '0' '1' '0' '1' '1' '0']
['0111' '0' '0' '1' '0' '0' '0' '0' '0' '0' '1' '0' '0' '1' '0']
['1000' '0' '0' '0' '0' '0' '1' '0' '1' '0' '0' '1' '0' '0' '1']
['1001' '1' '0' '0' '0' '0' '0' '1' '0' '0' '1' '0' '1' '1' '0']
['1010' '1' '0' '0' '0' '1' '0' '0' '0' '0' '1' '0' '1' '1' '0']
['1011' '1' '0' '0' '0' '0' '0' '0' '0' '0' '1' '0' '0' '1' '0']
['1100' '0' '0' '0' '0' '0' '1' '0' '1' '0' '0' '1' '0' '0' '1']
['1101' '0' '0' '0' '0' '0' '0' '1' '0' '0' '0' '0' '1' '1' '0']
['1110' '0' '0' '0' '0' '1' '0' '0' '0' '0' '0' '0' '1' '1' '0']
['1111' '0' '0' '0' '0' '0' '0' '0' '0' '0' '1' '0' '1' '1' '0']

I want to sum all elements of each row excluding index 0 (the 4 digit numbers). And then store those sums in a list.

This is what my list of sums should look like:

[1, 4, 4, 4, 4, 4, 5, 5, 3,.......,3] (Imagine it was all filled with the right sums)

However, this is what my code outputs:

number of rows: 16
number of cols: 15
num1s before: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
num1s after : [3, 3, 3, 3, 3, 3, 3, 3, 3, 7, 3, 7, 9, 7]

I'm not sure what the error is, but I think it has to do with string/int conversion. Since my table is in strings, but I convert it to ints for summing. Debugging it shows the correct results, so I'm not sure where the error is.

Here is my code:

import numpy

print ("Reading..")
txtfile = open("test1.txt", "r")
print(txtfile.readline())
txtfile.close()

r= numpy.genfromtxt('test1.txt',dtype=str,skiprows=1)

for x in range (0,len(r)):
    print(r[x])

allTested = [0] * (len(r[0]) - 1)
num1s = [0] * (len(r[0]) - 1)

print("number of rows:", len(r))
print("number of cols:", len(r[0]))
print("num1s before:",num1s)

for x in range (0,len(r)):
    for y in range(1,len(r[0])):
        num1s[y-1] += int(r[x][y])


print("num1s after :",num1s)

AB_IM · Accepted Answer · 2021-04-28 02:30:57Z

10

You're over-complicating it. Instead try:

np.sum(array,axis=1).tolist()

this should return a list which contain the sum of all rows

ex:

import numpy as np
array = np.array([range(10),range(10),range(10),range(10)])

sum_ = np.sum(array,axis=1).tolist()

print sum_
print type(sum_) 

>> [45, 45, 45, 45]
>> <type 'list'>

edited Apr 28, 2021 at 2:30

AB_IM

3743 silver badges21 bronze badges

answered May 22, 2015 at 2:13

farhawa

10.5k16 gold badges58 silver badges93 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

KHMB Over a year ago

Haha brother I know I must be complicating a lot of things in python. Is that a command that generates a list? As in I don't need the nested for loop ?

farhawa Over a year ago

yeah .tolist() will generate a list and you don't need a loop for that. just try it

KHMB Over a year ago

Doesn't seem to be working. This is what I'm doing: w = numpy.sum(r,axis=1).tolist() and then printing w. I get "cannot perform reduce with flexible type" when I run it. Would you mind editing my code and showing me how you do it? I'm most likely implementing it incorrectly.

farhawa Over a year ago

@user4927176 ok just declare your array as an array of floats this way r= numpy.genfromtxt('test1.txt',dtype=float, skiprows=1)

KHMB Over a year ago

I would love to declare my array as int. But I want the first element of each row to remain the same size it is. If I do dtype= int it turns 0000 to 0, and 0001 to 1. Which I dont want. Is there a fix for that ?

KHMB · Accepted Answer · 2015-05-22 03:24:10Z

2

Okay. Figured out the answer.

@wajid Farhani was close, but it wasn't working in my case.

His command for np.sum works, but I had to perform some indexing so I can ignore index 0 of every row. My issue was that I thought indexing 2D array was done by array[x][y], when it's array[x,y].

Fixed code:

import numpy

print ("Reading..")
txtfile = open("test1.txt", "r")
print(txtfile.readline())
txtfile.close()

r= numpy.genfromtxt('test1.txt',dtype=str,skiprows=1)

for x in range (0,len(r)):
    print(r[x])

allTested = [0] * (len(r[0]) - 1)
num1s = [0] * (len(r))

print("number of rows:", len(r))
print("number of cols:", len(r[0]))
print("num1s before:",num1s)

array = numpy.array(r,dtype=int)

s = numpy.sum(array[0:len(array),1:len(array[0])],axis=1).tolist()

print("num1s after :",s)

Correct output:

num1s before: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
num1s after : [1, 4, 4, 4, 4, 5, 5, 3, 4, 5, 5, 3, 4, 3, 3, 3]

answered May 22, 2015 at 3:24

KHMB

511 gold badge1 silver badge5 bronze badges

2 Comments

farhawa Over a year ago

happy that my answer helped you. One more thing, it's wajdi not wajid :)

Imanol Luengo Over a year ago

You are over complicating array indexing. s = numpy.sum(array[:, 1:], axis=1).tolist() would do the same.

Collectives™ on Stack Overflow

Sum elements in a row (Python/Numpy)

2 Answers 2

5 Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related