NumPy ndarray.searchsorted() Method

NumPy ndarray.searchsorted()

The numpy.ndarray.searchsorted() method finds the indices where elements should be inserted to maintain order. It works on sorted arrays and allows inserting elements from the left or right side of existing values.

Syntax

ndarray.searchsorted(v, side='left', sorter=None)

Parameters

Parameter	Type	Description
v	1-D array_like	Values to insert into the sorted array.
side	{‘left’, ‘right’}, optional	Specifies whether to insert at the leftmost or rightmost suitable index. Default is 'left'.
sorter	1-D array_like, optional	An array of indices that sort ndarray. Useful for searching in an indirectly sorted array.

Return Value

Returns an integer or an array of integers indicating the indices where elements should be inserted while preserving order.

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Examples

1. Basic Usage of ndarray.searchsorted()

Find the index where a value should be inserted in a sorted array.

import numpy as np

# Sorted input array
arr = np.array([1, 3, 5, 7])

# Value to insert
value = 4

# Finding the insertion index
index = arr.searchsorted(value)

# Printing the result
print(index)  # Output: 2 (4 should be inserted at index 2 to maintain order)

Output:

2

2. Using the side Parameter

Specifying whether to insert on the leftmost or rightmost occurrence of the existing values.

import numpy as np

# Sorted input array with duplicate values
arr = np.array([1, 2, 2, 3, 5])

# Value to insert
value = 2

# Inserting on the left
left_index = arr.searchsorted(value, side='left')

# Inserting on the right
right_index = arr.searchsorted(value, side='right')

# Printing results
print(left_index)   # Output: 1 (Inserts before the first occurrence of 2)
print(right_index)  # Output: 3 (Inserts after the last occurrence of 2)

Output:

1
3

3. Searching for Multiple Values

Using an array of values to find multiple insertion indices.

import numpy as np

# Sorted input array
arr = np.array([10, 20, 30, 40])

# Values to insert
values = np.array([25, 35, 5])

# Finding the insertion indices
indices = arr.searchsorted(values)

# Printing results
print(indices)  # Output: [2 3 0] (Each value's correct insertion index)

Output:

[2 3 0]

4. Using the sorter Parameter

Searching within an indirectly sorted array by providing a sorter array.

import numpy as np

# Unsorted input array
arr = np.array([30, 10, 20, 40])

# Indices that sort the array
sorter = np.argsort(arr)

# Values to insert
values = np.array([25, 35])

# Finding the insertion indices using sorter
indices = arr.searchsorted(values, sorter=sorter)

# Printing results
print(indices)  # Output: [2 3] (Based on sorted order of arr: [10, 20, 30, 40])

Output:

[2 3]