Channel operator that returns count of elements so far.

[siddharthab]

Currently, the reduce operator returns the final accumulated value, but a channel of the intermediate values would also be useful. A simplest use case could be to return the count of items processed so far.

This is similar to the scan function in the under-preview recursion features, but is based on Groovy closures alone.

I imagine people currently do something like the below, but I am not sure if the increments to num_items needs to be synchronized or if only a single thread ever touches the variable.

num_items = 0
ch.map { num_items++ }

[bentsherman]

There is a scan operator in nf-boost if you'd like to try it. At some point I plan to merge it into Nextflow but it might be a while

[siddharthab]

Excellent. It's exactly what I was looking for.