Type of array index?

New to Julia
13

I think you are a bit too hung up on the type of indices. You can index into an array using whatever Integer type you want:

1.7.1> a = rand(5);

1.7.1> a[UInt8(3)]
0.45629312424449464

1.7.1> a[big(3)]
0.45629312424449464

1.7.1> a[3]
0.45629312424449464

So the index type is not something that you should concern yourself with in almost any case. Just use Int, which corresponds to the default machine integer type on your system (64 or 32 bit).

They keytype function exists, but as its docstring says, it

is provided mainly for compatibility with the dictionary interface.

Don’t think about it. And anyway, you should use findall for this.

Edit: But, okay, let’s say you really need this, for some reason. Then you can still use whatever integer type you want:

idx = UInt[]
for i in eachindex(v)
    push!(idx, i)

will work, and so will

idx = Int8[]
for i in eachindex(v)
    push!(idx, i)

since i is converted into eltype(idx) when you push!. You just have to make sure that the integer type is big enough to hold the values you need.

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