Hi,

Suppose I have an array `a`

like the following

```
5Γ2 Matrix{Float64}:
2.0 1.0
3.0 0.0
4.0 1.0
2.0 0.0
4.0 1.0
```

The second column can only be 0 or 1. Now I want to pick the rows whose second element is 0 and store the first elements of these rows into a new array. In the example, I should have

```
b =[3.0,4.0]
```

How to achieve this goal?

Also, since my second column can only have 0 or 1. So in principle I can use Boolean variables. How to initiate my array such that the first column is 0(float64) and the second column is false (Bool).

Thanks