How to access columns in NumPy array

You can easily access columns in the NumPy array with the following code. If you want to learn Python, I highly recommend reading This Book.

Method 1: Using Slices

In this method, I will use slices to access single, and multiple columns. The index starts from 0.

Example 1: Access single column

# Import NumPy library
import numpy as np

# Make a NumPy array
a = np.array([[1, 2, 3, 4, 5],
              [2, 4, 6, 8, 10],
              [3, 4, 5, 6, 7]])

# Display 4th Column using Slices
print(a[:,3])

[4 8 6]

Example 2: Access sequential multiple columns

# Import NumPy library
import numpy as np

# Make a NumPy array
a = np.array([[1, 2, 3, 4, 5],
              [2, 4, 6, 8, 10],
              [3, 4, 5, 6, 7]])

# Display 4th and 5th Column using Slices
print(a[:,3:5])

[[ 4  5]
 [ 8 10]
 [ 6  7]]

Example 3: Access random multiple columns

# Import NumPy library
import numpy as np

# Make a NumPy array
a = np.array([[1, 2, 3, 4, 5],
              [2, 4, 6, 8, 10],
              [3, 4, 5, 6, 7]])

# Display 2nd and 5th Column using Slices
print(a[:,[1,4]])

[[ 2  5]
 [ 4 10]
 [ 4  7]]

Method 2: Using Ellipsis

In this method, I will display the 5th column of the NumPy array using ellipsis. The index starts from 0.

# Import NumPy library
import numpy as np

# Make a NumPy array
a = np.array([[1, 2, 3, 4, 5],
              [2, 4, 6, 8, 10],
              [3, 4, 5, 6, 7]])

# Display 5th Column using Ellipsis
print(a[..., 4])