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How to Set Axis for Rows and Columns in NumPy ?

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  • Difficulty Level : Expert
  • Last Updated : 30 May, 2021
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In this article, we are going to see how to set the axis for rows and columns in NumPy.

Functions Used

  • np.array(object): to create a NumPy array, the object is the parameter that contains the array
  • np.reshape(rows, columns): to reshape the array into the specified number of rows and columns. Here in the below examples, we have given -1 in place of rows to let numpy figure it out if there are 3 columns in each row.
  • np.sum(axis): to calculate the sum or addition of the elements. Here we have mentioned the axis to do the operation array-wise, row-wise, or column-wise as per requirement.

Example 1: Set axis for array-wise calculation

In this example, we will reshape the NumPy array into rows having 3 columns each i.e nparray.reshape(-1, 3) to make it two-dimensional. Then we will perform the sum operation of the array elements array-wise that is in normal order starting from the first to last element of the NumPy array. We specifically set the axis= None to trigger the normal array-wise operation.

Code:

Python3




import numpy as np
nparray = np.array([[1, 2, 3], [11, 22, 33],
                    [4, 5, 6], [8, 9, 10], 
                    [20, 30, 40]])
  
nparray = nparray.reshape(-1, 3)
print(nparray)
  
# calculating sum along 
# axix=None i.e array-wise
output = nparray.sum(axis=None)
print("\n\nSum array-wise: ", output)

Output :

[[ 1  2  3]
 [11 22 33]
 [ 4  5  6]
 [ 8  9 10]
 [20 30 40]]


Sum array-wise:  204

Example 2: Set axis for column-wise calculation

In this example, we will reshape the numpy array into rows having 3 columns each. Then performe the sum operation of the array elements using the sum() function column-wise. We specifically set the axis= 0 to trigger the normal array-wise operation.

Code:

Python3




import numpy as np
  
  
nparray = np.array([[1, 2, 3], [11, 22, 33],
                    [4, 5, 6], [8, 9, 10],
                    [20, 30, 40]])
nparray = nparray.reshape(-1, 3)
print(nparray)
  
# calculating sum along axix=0 
# i.e column-wise
output = nparray.sum(axis = 0)
print("\n\nSum column-wise: ", output)

Output :

[[ 1  2  3]
 [11 22 33]
 [ 4  5  6]
 [ 8  9 10]
 [20 30 40]]


Sum column-wise:  [44 68 92]

Example 3: Set axis for row-wise calculation

We will specifically set the axis = 1 to trigger the normal row-wise calculation.

Code:

Python3




import numpy as np
nparray = np.array([[1, 2, 3], [11, 22, 33],
                    [4, 5, 6], [8, 9, 10], 
                    [20, 30, 40]])
  
nparray = nparray.reshape(-1, 3)
print(nparray)
  
# calculating sum along axix=1 
# i.e row0wise
output = nparray.sum(axis = 1)
print("\n\nSum row-wise: ", output)

Output :

[[ 1  2  3]
 [11 22 33]
 [ 4  5  6]
 [ 8  9 10]
 [20 30 40]]


Sum row-wise:  [ 6 66 15 27 90]

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