Numpy aggregate functions mean() to get mean value of elements with different options

numpy.mean(a,axis=None,dtype=None,out=None,keepdims=False)

Return arithmetic mean of elements across given axis.

`a`	array, elements to get the mean value
`axis`	Int (optional ), or tuple, default is None. If axis given then across the axis is returned.
`dtype`	data-type( Optional ), Data Type of returned array or value.
`out`	Optional. If given then output to be stored. Must be of same time as of the output
`keepdims`	Bool ( Optional ), output matches to the input array dimension.

We will use these parameters in our examples.

Sample array

You can use randint() to create an array for our examples. Or can use fixed elements to create the array.

import numpy as np
# my_data=np.random.randint(2,high=7,size=(3,3),dtype='int16') 
my_data=np.array([[6, 3, 2], [2, 6, 2], [6, 2, 3]])
print(my_data)

Output

[[6 3 2]
 [2 6 2]
 [6 2 3]]

Axis

Sum of the elements across the axis. Axis of Numpy array

print("mean()      : ", my_data.mean())
print("mean(axis=0):", my_data.mean(axis=0))
print("mean(axis=1):", my_data.mean(axis=1))

Output

mean()      :  3.5555555555555554
mean(axis=0): [4.66666667 3.66666667 2.33333333]
mean(axis=1): [3.66666667 3.33333333 3.66666667]

dtype

The data type of the output. By default the output will have the dtype of input array.

print("mean(axis=1,dtype=np.int8) : ", my_data.mean(axis=1,dtype=np.int8))
print("mean(axis=1,dtype=np.int32) : ", my_data.mean(axis=1,dtype=np.int32))
print("mean(axis=1,dtype=np.float64) : ", my_data.mean(axis=1,dtype=np.float64))
print("mean(axis=1,dtype=np.complex128) : ", my_data.mean(axis=1,dtype=np.complex128))

Output

mean(axis=1,dtype=np.int8) :  [3 3 3]
mean(axis=1,dtype=np.int32) :  [3 3 3]
mean(axis=1,dtype=np.float64) :  [3.66666667 3.33333333 3.66666667]
mean(axis=1,dtype=np.complex128) :  [3.66666667+0.j 3.33333333+0.j 3.66666667+0.j]

keepdims

If it is set to True ( keepdims=True ) then it will take the dimension of input array.

print("mean(keepdims=True) : ", my_data.mean(keepdims=True))
print("mean(keepdims=False) : ", my_data.mean(keepdims=False))

Output

mean(keepdims=True) :  [[3.55555556]]
mean(keepdims=False) :  3.5555555555555554

out

Alternative output array, must be of same shape as expected output. Let us first check with axis.

x = np.zeros(3,dtype=int)
print(my_data.mean(axis=0,out=x))
print(x)

Output

[4 3 2]
[4 3 2]

Without using axis

y = np.array(1)
print(my_data.mean(out=y))
print(y)

Output

3
3

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Numpy mean()

Sample array

Axis

dtype

keepdims

out

Subhendu Mohapatra