renegade - 4 months ago 22

Python Question

I have the following situation:

`>>> a # I have`

array([[0, 1],

[0, 2],

[0, 2],

[1, 3],

[1, 3],

[2, 1]])

>>> new_a # I want to get to

array([[0, 1],

[1, 3],

[2, 1]])

Basically a pure numpy solution on how to remove the entire row IF there are duplicate entries in the first column. For example: The first row is [0, 1], and the second is [0,2] -- Since the 0 (first column) is duplicated, I would like to keep the first instance and remove any other ones.

I'm sure I could set up some If statements and while loops -- but I am wondering if there are more elegant solutions. Thanks!

Answer

Here's one way to do it with `np.unique`

, taking indices of unique items along the first column and then slicing the array along the first axis with the indices:

```
_, indices = np.unique(arr[:, 0], return_index=True)
print(arr[indices, :])
# [[0 1]
# [1 3]
# [2 1]]
```