Assume I have an array:

```
a = np.array([1,2,3,4,5])

```

Now I want to find the indices of elements in this array corresponding to the values given by another array input:

```
input = np.array([2,4,5])

```

The expected result should be:

```
result = [1,3,4]

```

A boolean mask, which is true for element indices 1,3,4 would also be fine.

I do not want to use looping to solve this. I assume that a possible solution has to do with the numpy where() function, but using this one, I am only able to compare the entries of array a with one element of array input at a time. Because the length of input might differ, I cannot really use this approach. Do you have any other ideas?

Thanks in advance.