# How to replace one column by a value in a numpy array?

Hello Guys, How are you all? Hope You all Are Fine. Today We Are Going To learn about How to replace one column by a value in a numpy array in Python. So Here I am Explain to you all the possible Methods here.

## How to replace one column by a value in a numpy array?

1. How to replace one column by a value in a numpy array?

Here `a[:, 0]` means “select all rows from column 0”. The value `1` is broadcast across this selected column, producing the desired array (it's not necessary to use a list `[1, 1]`, although you can).

2. replace one column by a value in a numpy array

Here `a[:, 0]` means “select all rows from column 0”. The value `1` is broadcast across this selected column, producing the desired array (it's not necessary to use a list `[1, 1]`, although you can).

## Method 1

You can replace the first column as follows:

```>>> a = np.zeros((2,2), dtype=np.int)
>>> a[:, 0] =  1
>>> a
array([[1, 0],
[1, 0]])
```

Here `a[:, 0]` means “select all rows from column 0”. The value `1` is broadcast across this selected column, producing the desired array (it’s not necessary to use a list `[1, 1]`, although you can).

Your syntax `a[:][0]` means “select all the rows from the array `a` and then select the first row”. Similarly, `a[0][:]` means “select the first row of `a` and then select this entire row again”. This is why you could replace the rows successfully, but not the columns – it’s necessary to make a selection for axis 1, not just axis 0.

## Method 2

You can do something like this:

```import numpy as np

a = np.zeros((2,2), dtype=np.int)
a[:,0] = np.ones((1,2), dtype=np.int)```

## Conclusion

It’s all About this issue. Hope all Methods helped you a lot. Comment below Your thoughts and your queries. Also, Comment below which Method worked for you? Thank You.