Fancy indexing is a method used when working in arrays. It is an advanced form of simple indexing. An index is used to represent the position of an element within a given array. Fancy indexing is used to get multiple elements by passing a list of indices. For example, given a list of numbers, the position of any of the elements in the list can easily be found by passing an index as shown below:
#import numpy libraryimport numpy as np#creating an array, XX = np.array([1, 12, 31, 4, 50, 6, 7, 28, 9, 20])#returning the number in the fifth positionprint(X[4]) #python index begins from zero
The code above demonstrates simple indexing in NumPy:
Line 2: We import the NumPy library as np.
Line 5: We pass a list of numbers into the np.array() function and assign it to the variable, X. This creates a NumPy array.
Line 8: We use the print() method to pass the index [4], into the previously created array, X. Then we print the results. This returns the number at the fifth position, 50.
In the code above, we pass the index, 4, to return the number in the fifth position, 50. We can use a list of indices to return the numbers in the first, fourth, fifth, and eighth position. We do so by using the list, X, and a list of indices, y.
#import numpy libraryimport numpy as np#creating an array, XX = np.array([1, 12, 31, 4, 50, 6, 7, 28, 9, 20])#list of indices, Yy = [0,3,4,7]#fancy indexingprint(X[y])
The code above demonstrates fancy indexing in NumPy:
Line 2: We import the NumPy library as np.
Line 5: We pass a list of numbers into the np.array() function and assign it to the variable, X. This creates a NumPy array.
Line 8: We assign a list of indices corresponding to the first, fourth, fifth, and eighth position to the variable, y.
Line 11: We use the print() method to pass y as an index into X and print it. Then, we print the list of numbers corresponding to the index positions in y to the console.
Fancy indexing enables the selection of multiple elements at once. It also eliminates the problem of repetition when returning multiple elements from an array by index.
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