How to use where() Method In Python
where() method is used to specify the index of a particular element specified in the condition.
Syntax: numpy.where(condition[, x, y])
Example 1: Get index positions of a given value
Here, we find all the indexes of 3 and the index of the first occurrence of 3, we get an array as output and it shows all the indexes where 3 is present.
Python3
# import numpy packageimport numpy as np# create an numpy array a = np.array([1, 2, 3, 4, 8, 6, 7, 3, 9, 10])# display index value of 3print("All index value of 3 is: ", np.where(a == 3)[0])print("First index value of 3 is: ",np.where(a==3)[0][0]) |
Output:
All index value of 3 is: [2 7] First index value of 3 is: 2
Example 2: Print First Index Position of Several Values
Here, we are printing the index number of all values present in the values array.
Python3
# import numpy packageimport numpy as np# create an numpy array a = np.array([1, 2, 3, 4, 8, 6, 2, 3, 9, 10])values = np.array([2, 3, 10]) # index of first occurrence of each valuesorter = np.argsort(a)print("index of first occurrence of each value: ", sorter[np.searchsorted(a, values, sorter=sorter)]) |
Output:
index of first occurrence of each value: [1 2 9]
Example 3: Get the index of elements based on multiple conditions
Get the index of elements with a value less than 20 and greater than 12
Python3
# Create a numpy array a = np.array([11, 12, 13, 14, 15, 16, 17, 15, 11, 12, 14, 15, 16, 17, 18, 19, 20])# Get the index of elements with value less # than 20 and greater than 12print("Index of elements with value less\ than 20 and greater than 12 are: \n", np.where((a > 12) & (a < 20))) |
Output:
Index of elements with value less than 20 and greater than 12 are: (array([ 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 15], dtype=int64),)
How to find the Index of value in Numpy Array ?
In this article, we are going to find the index of the elements present in a Numpy array.
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