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How to get column in Numpy array?

Posted on March 29, 2021January 4, 2023 By Luke K

Let’s learn how to get a column in a Numpy array. This is what allows you to manipulate data in the Numpy Python library.numpy how to get column

We have such a Numpy array:

[1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 1.10],
[2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 2.10],
[3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 3.10]

How to get a single column?

How to get only the elements from the fourth column? Like that:

import numpy as np

my_array = np.array((
    [1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 1.10],
    [2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 2.10],
    [3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 3.10]))

chosen_elements = my_array[:, 3]

print(chosen_elements)

numpy how to get column

chosen_elements = my_array [:, 3] each (colon) element from the fourth column is returned (3 means fourth column because computers start counting from 0).

See also  How to concatenate arrays in Numpy?

How to get one value from given column and row?

Keep moving further.

How to get elements from the second row and fourth column?

import numpy as np

my_array = np.array((
    [1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 1.10],
    [2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 2.10],
    [3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 3.10]))

chosen_elements = my_array[1, 3]

print(chosen_elements)

numpy how to get row and column

chosen_elements = my_array[1, 3] returned second row and fourth column.

See also  How to find common part of arrays in Numpy?

How to get multiple columns?

So, how do you get a lot of columns? Let’s get columns two through six.

import numpy as np

my_array = np.array((
    [1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 1.10],
    [2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 2.10],
    [3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 3.10]))

chosen_elements = my_array[:, 1:6]

print(chosen_elements)

numpy how to get many columns

chosen_elements = my_array[:, 1:6] is returning columns second to sixth thanks to colon. A colon denotes a range of 1 to 6 columns, 2 to 6.

How to get every few columns

One more tip.

See also  How to rotate a matrix?

How to get many columns from a step? Let’s return to columns second to sixth, but every second column.

import numpy as np

my_array = np.array((
    [1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 1.10],
    [2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 2.10],
    [3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 3.10]))

chosen_elements = my_array[:, 1:6:2]

print(chosen_elements)

numpy how to get many columns with a step

chosen_elements = my_array[:, 1:6:2] as you can notice added a step. Another colon is doing that, and digit 2 tells how big the step is.

Now you can get columns in Numpy arrays.

numpy Tags:array, column, step

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