Let’s say I have matrix that contains 5 rows and 4 columns:

```
arr = [[1,1,1,1],
[2,2,2,2],
[3,3,3,3],
[4,4,4,4],
[5,5,5,5]]
```

and I want to randomly zero=out/mask a certain percentage of this matrix row-wise. So if I set the percentage to be zeroed to 40%. I will get the following:

```
arr = [[0,0,0,0],
[2,2,2,2],
[3,3,3,3],
[0,0,0,0],
[5,5,5,5]]
```

what would be a good way to achieve this? Thanks!

### >Solution :

One way to achieve your task is following (set `num_zero_rows`

):

```
import random
arr = [[1,1,1,1],
[2,2,2,2],
[3,3,3,3],
[4,4,4,4],
[5,5,5,5]]
num_zero_rows = 2
zero_idxs = set(random.sample(range(len(arr)), num_zero_rows))
arr = [([0] * len(arr[i]) if i in zero_idxs else arr[i])
for i in range(len(arr))]
print(arr)
```

Output:

```
[[0, 0, 0, 0], [2, 2, 2, 2], [0, 0, 0, 0], [4, 4, 4, 4], [5, 5, 5, 5]]
```