Function like enumerate to get index and value for offset arrays?

Question

If I have an array like this:

using OffsetArrays

a = OffsetArray(collect(1:5),(11:15))

I can iterate through the array with:

for (i,x) in enumerate(a)
    println((i,x))
end

and get:

(1, 1)
(2, 2)
(3, 3)
(4, 4)
(5, 5)

But I want this:

(11, 1)
(12, 2)
(13, 3)
(14, 4)
(15, 5)

Is there a way to get the real index since I am using an offset array?

Answer 1

The function pairs respects the indexing behaviour:

julia> using OffsetArrays

julia> a = OffsetArray(collect(1:5),(11:15))

julia> for (i,x) in pairs(a)
         println((i,x))
       end

(11, 1)
(12, 2)
(13, 3)
(14, 4)
(15, 5)

from the docs:

Base.pairs — Function.

pairs(collection)

Return an iterator over key => value pairs for any collection that maps a set of keys to a set of values. This includes arrays, where the keys are the array indices.

pairs(IndexLinear(), A)
pairs(IndexCartesian(), A)
pairs(IndexStyle(A), A)

An iterator that accesses each element of the array A, returning i => x, where i is the index for the element and x = A[i]. Identical to pairs(A), except that the style of index can be selected. Also similar to enumerate(A), except i will be a valid index for A, while enumerate always counts from 1 regardless of the indices of A.

Specifying IndexLinear() ensures that i will be an integer; specifying IndexCartesian() ensures that i will be a CartesianIndex; specifying IndexStyle(A) chooses whichever has been defined as the native indexing style for array A.

Mutation of the bounds of the underlying array will invalidate this iterator.