Findall() not behaving well for an array of size 1

General Usage
1

Hi, I was just implementing a code for my work and inside a very long code, I had used findall() to find the set of numbers that satisfy certain property. But I found an unexpected result and when I tried debugging the code found this behaviour. Which feels to be wrong.

nums=[1,2,3]
test=[1,2,3,4,5,6]
choicenonnums=findall(x->x∉nums,test)

This provides the right output, which is all the numbers in the array test that are not in nums array.

julia> choicenonnums=findall(x->x∉nums,test)
3-element Vector{Int64}:
 4
 5
 6

But when I change the test array as a single number array. Or an array of length 1. It gives [1] as output.

julia> test=[75]
1-element Vector{Int64}:
 75

julia> choicenonnums=findall(x->x∉nums,test)
1-element Vector{Int64}:
 1

Is this some obscure use of findall() that I am not aware of? Or is this a bug?

2

findall returns the indices of the elements satisfying the condition (not the elements themselves). And element 1 of test is the number 75, which is not in [1,2,3], thus that’s what’s expected.

1 Like
3

Thanks I forgot that line of the code. That is the solution

4

Additionally, if it is the values you want to have you can just replace findall with filter in these examples.

5

Or alternatively, for this specific usage:

julia> setdiff(test, nums)
3-element Vector{Int64}:
 4
 5
 6