# findin

findin(a, b)

Returns the indices of elements in collection `a` that appear in collection `b`

## Examples

``````julia> findin([1,2,2],[2,4,5])
2-element Array{Int64,1}:
2
3``````
``````julia> findin([1,2,3],[2,4,5])
1-element Array{Int64,1}:
2

julia> foo = [2, 5, 7, 5, 2, -1];
julia> bar = [2, 5, 4];
julia> findin(bar, foo)
1
2``````
``````julia> a = [10, 20, 30, 40, 50];
julia> b = [20, 40, 60];
julia> findin(a, b)
2-element Array{Int64,1}:
2
4``````

In this example, the function `findin` returns the indices of elements in the collection `a` that appear in the collection `b`. The elements 20 and 40 are present in both `a` and `b`, so their indices [2, 4] are returned.

``````julia> names = ["Alice", "Bob", "Charlie", "David"];
julia> search_names = ["Charlie", "Frank"];
julia> findin(names, search_names)
1-element Array{Int64,1}:
3``````

Here, the function `findin` is used to find the indices of elements in the `names` array that appear in the `search_names` array. Only "Charlie" is present in both arrays, so its index 3 is returned.

Common mistake example:

``````julia> fruits = ["apple", "banana", "orange"];
julia> findin(fruits, "apple")
ArgumentError: `findin` requires the second argument to be an iterable collection, found String``````

In this example, the second argument to `findin` should be an iterable collection, but a single string was provided instead. Make sure to pass a collection as the second argument to avoid this error.