.var()

Published Apr 23, 2024
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The .var() function computes the variance of the elements in an array, either across all elements or along a specified axis (if provided). Variance is a statistical measurement that shows how far each number in the array is spread out from the mean. In other words, it measures the dispersion or spread in the data.

A high variance indicates that the numbers in the array are far from the mean, while a low variance indicates that they are close to the mean.

Syntax

numpy.var(array, axis=None)
  • array: The array for which the variance is to be calculated.
  • axis: An optional parameter that specifies the axis along which the variance is to be calculated.

If axis is not specified, the variance is calculated for the entire (flattened) array. If axis is specified, then the variance is calculated along that axis. For a 2D array, if axis=0, the variance is calculated column-wise, and if axis=1, the variance is calculated row-wise.

Example

The following example creates a 2D array and calculates the overall variance (variance of the flattened array), column-wise variance, and row-wise variance of the array using the .var() function:

import numpy as np
# Creating a 2D array
array_2d = np.array([[1, 2, 3],[4, 5, 6],[7, 8, 9]])
# Calculating the overall variance
overall_variance = np.var(array_2d)
print(overall_variance)
# Calculating the column-wise variance (axis=0)
column_variance = np.var(array_2d, axis=0)
print(column_variance)
# Calculating the row-wise variance (axis=1)
row_variance = np.var(array_2d, axis=1)
print(row_variance)

This produces the following output:

6.666666666666667
[6. 6. 6.]
[0.66666667 0.66666667 0.66666667]

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