Calculate the sum of all columns in a 2D NumPy array
Last Updated :
21 Jul, 2021
Let us see how to calculate the sum of all the columns in a 2D NumPy array.
Method 1 : Using a nested loop to access the array elements column-wise and then storing their sum in a variable and then printing it.
Example 1:
Python3
import numpy
def colsum(arr, n, m):
for i in range (n):
su = 0 ;
for j in range (m):
su + = arr[j][i]
print (su, end = " " )
TwoDList = [[ 1 , 2 , 3 ], [ 4 , 5 , 6 ],
[ 7 , 8 , 9 ], [ 10 , 11 , 12 ]]
TwoDArray = numpy.array(TwoDList)
print ( "2D Array:" )
print (TwoDArray)
print ( "\nColumn-wise Sum:" )
colsum(TwoDArray, len (TwoDArray[ 0 ]), len (TwoDArray))
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Output :
2D Array:
[[ 1 2 3]
[ 4 5 6]
[ 7 8 9]
[10 11 12]]
Column-wise Sum:
22 26 30
Example 2 :
Python3
import numpy
def colsum(arr, n, m):
for i in range (n):
su = 0 ;
for j in range (m):
su + = arr[j][i]
print (su, end = " " )
TwoDList = [[ 1.2 , 2.3 ], [ 3.4 , 4.5 ]]
TwoDArray = numpy.array(TwoDList)
print ( "2D Array:" )
print (TwoDArray)
print ( "\nColumn-wise Sum:" )
colsum(TwoDArray, len (TwoDArray[ 0 ]), len (TwoDArray))
|
Output :
2D Array:
[[1.2 2.3]
[3.4 4.5]]
Column-wise Sum:
4.6 6.8
Method 2: Using the sum() function in NumPy, numpy.sum(arr, axis, dtype, out) function returns the sum of array elements over the specified axis. To compute the sum of all columns the axis argument should be 0 in sum() function.
Example 1 :
Python3
import numpy
TwoDList = [[ 1 , 2 , 3 ], [ 4 , 5 , 6 ],
[ 7 , 8 , 9 ], [ 10 , 11 , 12 ]]
TwoDArray = numpy.array(TwoDList)
print ( "2D Array:" )
print (TwoDArray)
print ( "\nColumn-wise Sum:" )
print (numpy. sum (TwoDArray, axis = 0 ))
|
Output :
2D Array:
[[ 1 2 3]
[ 4 5 6]
[ 7 8 9]
[10 11 12]]
Column-wise Sum:
22 26 30
Example 2 :
Python3
import numpy
TwoDList = [[ 1.2 , 2.3 ], [ 3.4 , 4.5 ]]
TwoDArray = numpy.array(TwoDList)
print ( "2D Array:" )
print (TwoDArray)
print ( "\nColumn-wise Sum:" )
print ( * numpy. sum (TwoDArray, axis = 0 ))
|
Output :
2D Array:
[[1.2 2.3]
[3.4 4.5]]
Column-wise Sum:
4.6 6.8
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