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Get index of max value in numpy array python – Find max value & its index in Numpy Array | numpy.amax()

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Finding max value and it’s index in Numpy Array

Get index of max value in numpy array python: In this article we will discuss about how we can find max value and the index of that max value in Numpy array using numpy.amx().

numpy.amax( ) :

Syntax-numpy.amax(arr, axis=None, out=None, keepdims=<no value>, initial=<no value>)

Parameters :

  1. arr: Numpy array
  2. axis: This is an optional parameter unless provided flattens the array.

(Default: Returns the array of max values)

  1. Axis = 0: Returns array containing max values of each columns
  2. Axis = 1: Returns array containing max values of each rows

Let’s see one by one how to find it in 1D and 2D Numpy array.

Maximum value & its index in a 1D Numpy Array:

Numpy.amax: Let’s create a 1D numpy array from a list given below and find the maximum values and its index

Find maximum value:

Numpy find max index: To find the maximum value in the array, we can use numpy.amax( ) function and pass the array as function to it.

[10,5,19,56,87,96,74,15,50,12,98]
import numpy as np

# Finding the maximum value inside an array using amax( )
arr = np.array([10, 5, 19, 56, 87, 96, 74, 15, 50, 12, 98])
maxElem = np.amax(arr)
print("Max element : ", maxElem)

Output :
Max element :  98

Find index of maximum value :

np amax: To get the index of the max value in the array, we will have to use the where( ) function from the numpy library.

CODE:

import numpy as np

# Index of the maximum element
arr = np.array([10, 5, 19, 56, 87, 96, 74, 15, 50, 12, 98])
maxElem = np.amax(arr)
print("Max element : ", maxElem)
res = np.where(arr == np.amax(arr))
print("Returned result  :", res)
print("List of Indices of maximum element :", res[0])

Output :
Max element :  98
Returned result  : (array([10], dtype=int32),)
List of Indices of maximum element : [10]

Here, when we called the where( ) function, it returned us with a tuple of  arrays containing the indices of all the  values that follow our conditions.

Find maximum value & its index in a 2D Numpy Array

Numpy max value in array: We will use the following 2D array to demonstrate.

{50,59,54}

{45,46,78}

{98,20,24}

Find max value in complete 2D numpy array :

Numpy get index of max: When we are going to find the max value in a 2D numpy array, we can either do it by finding a single value or we can find column wise or row wise.

CODE:

import numpy as np

arr = np.array([[50, 59, 54], [45, 46, 78], [98, 20, 24]])
# Get the maximum value from the 2D array

maxValue = np.amax(arr)
print("The maximum value inside the array is", maxValue)

Output :
The maximum value inside the array is 98

Column or Row wise value

Numpy max value: To find the max value per each row, we can  pass axis =1 and for columns we can use axis =0.

CODE:

import numpy as np

arr = np.array([[50, 59, 54], [45, 46, 78], [98, 20, 24]])
# Get the maximum valuevin rows
maxRows = np.amax(arr, axis=1)
# Get the maximum valuevin columns
maxColumns = np.amax(arr, axis=0)

print(
    "The maximum values in rows are : ",
    maxRows,
    " and the maximum value in columns are : ",
    maxColumns,
)

Output :
The maximum values in rows are :  [59 78 98]  and the maximum value in columns are :  [98 59 78]

Find index of maximum value from 2D numpy array:

CODE:

import numpy as np

arr = np.array([[50, 59, 54], [45, 46, 78], [98, 20, 24]])
# Get the index of max value inside the 2D array
res = np.where(arr == np.amax(arr))
print("Tuple :", res)
print("Now Coordinates of max value in 2D array :")
# zipping both the arrays to find the coordinates
Coordinates = list(zip(res[0], res[1]))

for elem in Coordinates:
    print(elem)


Output :
Tuple : (array([2], dtype=int32), array([0], dtype=int32))
Now Coordinates Of max value in 2D array :
(2, 0)

numpy.amax() & NaN :

amax( ) also propagates the NaN values , which means if there is a NaN value present in the numpy array, then the max value returned by the function will be NaN.

import numpy as np

arr = np.array([[50, 59, np.NaN], [45, 46, 78], [98, 20, 24]])
# amax( ) propagating the NaN values

print("The max element in the numpy array is :", np.amax(arr))

Output :
The max element in the numpy array is : nan