Julia: enumerate from any index

[AlexanderKoshkarov]

it would be nice to have the ability to enumerate from any index like in python
now:

it = "hello"
for (i,el) in enumerate(it)
@show i
end

shows i=1,2...
would be nice to have:

it = "hello"
for (i,el) in enumerate(it,10)  # or enumerate(10,it)
@show i
end

shows i=10,11...

[ararslan]

It may also be useful to enumerate only up to a specific index. Perhaps keyword arguments like from= and to= could be used for this, e.g. enumerate(it, from=3, to=10). (Or maybe start and stop.) This functionality could probably be implemented fairly easily using take and drop from Base.Iterators.

[ararslan]

Seems like this can be accomplished simply and efficiently with zip(countfrom(n), x). See discussion in linked PR.

[nalimilan]

Note that starting from a specific index isn't really easy with the current iterators interface: next isn't guaranteed to accept the linear index as its state argument. So a fully generic implementation would have to call next i times to get the element number i. It would be nice to add an ind2state function which could be overridden for types which can offer a more efficient approach. That would also fix https://github.com/JuliaLang/julia/pull/18668 (see https://github.com/JuliaLang/julia/pull/18668#discussion_r80393729).

[sg1101]

I would like to work on this issue, please guide me how to proceed.

[KristofferC]

You implement the function, write tests for it and then make a Pull Request with the changes.

https://github.com/JuliaLang/julia/blob/master/CONTRIBUTING.md is a good read.