You can use the following methods to slice a 2D NumPy array:
Method 1: Select Specific Rows in 2D NumPy Array
#select rows in index positions 2 through 5 arr[2:5, :]
Method 2: Select Specific Columns in 2D NumPy Array
#select columns in index positions 1 through 3 arr[:, 1:3]
Method 3: Select Specific Rows & Columns in 2D NumPy Array
#select rows in range 2:5 and columns in range 1:3 arr[2:5, 1:3]
The following examples show how to use each method in practice with the following 2D NumPy array:
import numpy as np #create NumPy array arr = np.arange(24).reshape(6,4) #view NumPy array print(arr) [[ 0 1 2 3] [ 4 5 6 7] [ 8 9 10 11] [12 13 14 15] [16 17 18 19] [20 21 22 23]]
Example 1: Select Specific Rows of 2D NumPy Array
We can use the following syntax to select the rows in index positions 2 through 5:
#select rows in index positions 2 through 5 arr[2:5, :] array([[ 8, 9, 10, 11], [12, 13, 14, 15], [16, 17, 18, 19]])
Note that the syntax 2:5 tells NumPy to select rows 2 up to 5, but doesn’t include 5.
Thus, this syntax selects all of the values in the rows with index positions of 2, 3 and 4.
Example 2: Select Specific Columns of 2D NumPy Array
We can use the following syntax to select the columns in index positions 1 through 3:
#select columns in index positions 1 through 3 arr[, 1:3] array([[ 1, 2], [ 5, 6], [ 9, 10], [13, 14], [17, 18], [21, 22]]))
Note that the syntax 1:3 tells NumPy to select columns 1 up to 3, but doesn’t include 3.
Thus, this syntax selects all of the values in the columns with index positions of 1 and 2.
Example 3: Select Specific Rows & Columns of 2D NumPy Array
We can use the following syntax to select the rows in index positions 2 through 5 and the columns in index positions 1 through 3:
#select rows in 2:5 and columns in 1:3 arr[2:5, 1:3] array([[ 9, 10], [13, 14], [17, 18]])
This syntax returns all of the values in the 2D NumPy array between row index positions 2 through 5 and column index positions 1 through 3.
Additional Resources
The following tutorials explain how to perform other common operations in NumPy:
How to Find Index of Value in NumPy Array
How to Get Specific Column from NumPy Array
How to Add a Column to a NumPy Array
