You probably want something like this:

```
>>> a = np.array([True, True, True, False, False])
>>> b = np.array([[1,2,3,4,5], [1,2,3,4,5]])
>>> b[:,a]
array([[1, 2, 3],
[1, 2, 3]])
```

Note that for this kind of indexing to work, it needs to be an `ndarray`

, like you were using, not a `list`

, or it’ll interpret the `False`

and `True`

as `0`

and `1`

and give you those columns:

```
>>> b[:,[True, True, True, False, False]]
array([[2, 2, 2, 1, 1],
[2, 2, 2, 1, 1]])
```