NumPy strings.rfind()
The numpy.strings.rfind() function returns the highest index in a string where a specified substring is found, within an optional range. If the substring is not found, it returns -1.
Syntax
numpy.strings.rfind(a, sub, start=0, end=None)Parameters
| Parameter | Type | Description |
|---|---|---|
a | array-like (StringDType, bytes_, or str_ dtype) | The input string or array of strings. |
sub | array-like (StringDType, bytes_, or str_ dtype) | The substring to search for. |
start | array_like (integer dtype, optional) | The starting index of the range where the search is performed. Defaults to 0. |
end | array_like (integer dtype, optional) | The ending index (exclusive) of the range where the search is performed. Defaults to searching until the end of the string. |
Return Value
Returns an array of integers representing the highest index where the substring is found. If the substring is not found, it returns -1.
Examples
1. Finding the Last Occurrence of a Substring
Here, we search for the highest index where a substring appears in a given string.
import numpy as np
# Define the input string
string = np.array("hello world, welcome to the world of NumPy")
# Define the substring to search for
substring = np.array("world")
# Find the last occurrence of the substring
result = np.strings.rfind(string, substring)
# Print the result
print("Last occurrence index of 'world':", result)Output:
Last occurrence index of 'world': 24
The substring "world" appears twice, and the highest index where it appears is at position 24.
2. Searching Within a Range
We can limit the search within a specific range using the start and end parameters.
import numpy as np
# Define the input string
string = np.array("hello world, welcome to the world of NumPy")
# Define the substring to search for
substring = np.array("world")
# Define the search range (start at index 0, end at index 20)
result = np.strings.rfind(string, substring, start=0, end=20)
# Print the result
print("Last occurrence index of 'world' within range [0, 20]:", result)Output:
Last occurrence index of 'world' within range [0, 20]: 6
Since we restricted the search range to [0, 20], the function returns 6, which is the index of the first occurrence of "world".
3. Handling a Substring That Does Not Exist
If the substring is not found in the input string, the function returns -1.
import numpy as np
# Define the input string
string = np.array("hello world, welcome to NumPy")
# Define a substring that does not exist in the string
substring = np.array("Python")
# Try to find the last occurrence of the substring
result = np.strings.rfind(string, substring)
# Print the result
print("Index of non-existing substring 'Python':", result)Output:
Index of non-existing substring 'Python': -1
Since the substring "Python" does not appear in the string, the function returns -1.
4. Finding Substring Indices in an Array of Strings
We can use numpy.strings.rfind() on an array of strings to find the last occurrence of a substring in each element.
import numpy as np
# Define an array of strings
strings = np.array(["apple banana apple", "banana apple banana", "cherry banana apple"])
# Define the substring to search for
substring = np.array("banana")
# Find the last occurrence of 'banana' in each string
result = np.strings.rfind(strings, substring)
# Print the results
print("Last occurrence indices of 'banana' in each string:", result)Output:
Last occurrence indices of 'banana' in each string: [6 14 7]
The function finds the last occurrence of "banana" in each string within the array and returns their respective indices.