Searching Arrays
You can search an array for a certain value, and return the indexes that get a match.
To search an array, use the where() method.
Example
import numpy as np
arr = np.array([1, 2, 3, 4, 5, 4, 4])
x =
np.where(arr == 4)
print(x)
The example above will return a tuple: (array([3, 5, 6],)
Which means that the value 4 is present at index 3, 5, and 6.
Example
import numpy as np
arr = np.array([10, 14, 93, 41, 8, 7])
x =
np.where(arr%2 == 1)
print(x)
Example
import numpy as np
arr = np.array([10, 14, 93, 41, 8, 7])
x =
np.where(arr%2 == 0)
print(x)
Search Sorted
There is a method called searchsorted() which performs a binary search in the array, and returns the index where the specified value would be inserted to maintain the search order.
Note: The
searchsorted()method is assumed to be used on sorted arrays.
Example
import numpy as np
arr = np.array([6,
7, 8, 9])
x =
np.searchsorted(arr, 7)
print(x)
Example explained: The number 7 should be inserted on index 1 to remain the sort order.
The method starts the search from the left and returns the first index where the number 7 is no longer larger than the next value.
Search From the Right Side
By default the left most index is returned, but we can give side='right' to return the right most index instead.
Example
import numpy as np
arr = np.array([6,
7, 8, 9])
x =
np.searchsorted(arr, 7, side='right')
print(x)
Example explained: The number 7 should be inserted on index 2 to remain the sort order.
The method starts the search from the right and returns the first index where the number 7 is no longer less than the next value.
Multiple Values
To search for more than one value, use an array with the specified values.
Example
import numpy as np
arr = np.array([1,
3, 5, 7])
x =
np.searchsorted(arr, [2, 4, 6])
print(x)
The return value is an array: [1 2 3] containing the three indexes where 2, 4, 6 would be inserted in the original array to maintain the order.
