  # numpy.var () in Python

NumPy | Python Methods and Functions

` numpy.var (arr, axis = None) `: calculate the variance of the data (array elements) along the specified axis (if any).

Example:

x = 1 1 1 1 1
Standard Deviation = 0. Variance = 0

y = 9, 2, 5, 4, 12, 7, 8, 11, 9, 3, 7, 4, 12, 5, 4, 10, 9, 6, 9, 4

Step 1: Mean of distribution 4 = 7
Step 2: Summation of (x - x.mean ()) * * 2 = 178
Step 3: Finding Mean = 178/20 = 8.9
This Result is Variance.

Parameters :

arr: [array_like] input array.
axis: [int or tuples of int] axis along which we want to calculate the variance. Otherwise, it will consider ` arr ` to be flattened (works on all the axis). axis = 0 means variance along the column and axis = 1 means variance along the row.
out: [ndarray, optional] Different array in which we want to place the result. The array must have the same dimensions as expected output.
dtype: [data-type, optional] Type we desire while computing variance.

Results: Variance of the array (a scalar value if axis is none) or array with variance values ​​along specified axis.

Code # 1:

 ` # Python program illustrating ` ` # numpy.var () method ` ` import ` ` numpy as np `   ` # 1D array ` ` arr ` ` = ` ` [` ` 20 ` `, ` ` 2 ` `, ` ` 7 ` `, ` ` 1 ` `, ` ` 34 ` `] `   ` print ` ` (` ` "arr:" ` `, arr) ` ` print ` ` (` ` "var of arr:" ` `, np.var (arr)) ` ` `  ` print ` ` (` ` "var of arr:" ` `, np.var (arr , dtype ` ` = ` ` np.float32)) ` ` print ` ` (` ` "var of arr:" ` `, np.var ( arr, dtype ` ` = ` ` np.float64)) `

Output:

` arr: [20, 2, 7, 1, 34] var of arr: 158.16 var of arr: 158.16 var of arr: 158.16 `

Code # 2:

 ` # Python program illustrating ` ` # numpy.var () method ` ` import ` ` numpy as np `   ` # 2D array ` ` arr ` ` = ` ` [[` ` 2 ` `, ` ` 2 ` ` , ` ` 2 ` `, ` ` 2 ` `, ` ` 2 ` `], ` ` ` ` [` ` 15 ` `, ` ` 6 ` `, ` ` 27 ` `, ` ` 8 ` `, ` ` 2 ` `], ` ` [` ` 23 ` `, ` ` 2 ` `, ` ` 54 ` `, ` ` 1 ` `, ` ` 2 ` `,], ` ` [` ` 11 ` `, ` ` 44 ` `, ` ` 34 ` `, ` ` 7 ` `, 2 ]] ``     # var flattened array print ( "var of arr, axis = None:" , np.var (arr))     # var along the axis = 0 print ( "var of arr, axis = 0: " , np.var (arr, axis = 0 ))     # var along axis = 1 print ( "var of arr, axis = 1:" , np.va r (arr, axis = 1 ))  `

Output:

` var of arr, axis = None: 236.14000000000004 var of arr, axis = 0: [57.1875 312.75 345.6875 9.25 0.] var of arr, axis = 1: [0. 77.04 421.84 269.04] `