I need to get the last four column data of a `ndarray`, most of time code `arr[:, -4:]` is ok, but if the array just has one dimension, this will throw `IndexError: too many indices`.

My data is get with `arr = np.loadtxt('test.txt')`, so if `test.txt` has more than one line, like

```
0 1 2 3 4
0 10 20 30 40

```

everything is ok, but if `test.txt` has just one line, like

```
0 1 2 3 4

```

this will return `array([ 0, 1, 2, 3, 4])`, then `arr[:, -4:]` will throw exception, because it should be `arr[-4:]`, so how to make `loadtxt` return `array([[ 0, 1, 2, 3, 4]])`?