Repeat all the elements of a NumPy array of strings

Let us see how to repeat all elements of the given array of string 3 times. Example :

Input : [‘Akash’, ‘Rohit’, ‘Ayush’, ‘Dhruv’, ‘Radhika’] Output : [‘AkashAkashAkash’, ‘RohitRohitRohit’, ‘AyushAyushAyush’, ‘DhruvDhruvDhruv’, ‘RadhikaRadhikaRadhika’]

We will be using the numpy.char.multiply(a, i) method for this task.

numpy.char.multiply(a, i)

Syntax : numpy.char.multiply(a, i) Parameters : 

• a : array of str or unicode
• i : number of times to be repeated

Returns : Array of strings

Example 1 : Repeating 3 times. 

Python3

# importing the module
import numpy as np

# created array of strings
arr = np.array(['Akash', 'Rohit', 'Ayush',
                'Dhruv', 'Radhika'], dtype = np.str)
print("Original Array :")
print(arr)

# with the help of np.char.multiply()
# repeating the characters 3 times
new_array = np.char.multiply(arr, 3)
print("\nNew array :")
print(new_array)

Output : 

Original Array : [‘Akash’ ‘Rohit’ ‘Ayush’ ‘Dhruv’ ‘Radhika’] New array : [‘AkashAkashAkash’ ‘RohitRohitRohit’ ‘AyushAyushAyush’ ‘DhruvDhruvDhruv’ ‘RadhikaRadhikaRadhika’]

Time complexity: O(n), where n is the length of the input array
Auxiliary space: O(n).

Example 2: Repeating 2 times. 

Python3

# importing the module
import numpy as np

# created array of strings
arr = np.array(['Geeks', 'for', 'Geeks'])
print("Original Array :")
print(arr)

# with the help of np.char.multiply()
# repeating the characters 3 times
new_array = np.char.multiply(arr, 2)
print("\nNew array :")
print(new_array)

Output : 

Original Array :
['Geeks' 'for' 'Geeks']

New array :
['GeeksGeeks' 'forfor' 'GeeksGeeks']

Time complexity: O(n), where n is the number of characters in the original array.

Auxiliary space: O(n), where n is the number of characters in the original array. 

EXAMPLE 3 – Method 2: We can use a list comprehension to repeat each string in the array multiple times .

Python3

# importing the module
import numpy as np

# created array of strings
arr = np.array(['Geeks', 'for', 'Geeks'])
print("Original Array :")
print(arr)

# using list comprehension to repeat each string in the array
n = 2  # number of times to repeat each string
new_array = np.array([s * n for s in arr])
print("\nNew array :")
print(new_array)

OUTPUT- 

Original Array :
[‘Geeks’ ‘for’ ‘Geeks’]

New array :
[‘GeeksGeeks’ ‘forfor’ ‘GeeksGeeks’]

Time complexity: O(n * k), where n is the length of the input array and k is the number of times each string is repeated.
Auxiliary space: O(n), as we create a new list of length n to store the repeated strings. However, this is not counting the space needed for the input and output arrays.