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flatten_multiple_item_tuples_to_simple_tuple.md

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Flatten multiple-item tuple to 2-item tuple keeping key

It's common to have a channel with tuples that contain two items:

  • The first item is a string that represents an ID;
  • The second item is a list with multiple items that represents things related to the ID outside the list.

This is exactly what the fromFilePairs channel factory outputs, for example. Sometimes you need something slightly different, though. You still want something in a tuple together with an ID, but this something is a single item and you already have the data in the fromFilePairs format. How do you do that?

Channel
  .of(
      ['meta.1', [file('a'), file('b')]],
      ['meta.2', [file('a2'), file('b2'), file('c')]],
      ['meta.3', [file('a3')]],
  )
  .set { my_ch }

my_ch
  .flatMap { meta, files -> files.collect { [meta, it] } }
  .view()

The output should look like:

N E X T F L O W  ~  version 23.02.0-edge
Launching `flatten_tuple_w_multiple_items_keeping_key.nf` [furious_curran] DSL2 - revision: 90cacf091e
[meta.1, /Users/mribeirodantas/dev/sandbox/a]
[meta.1, /Users/mribeirodantas/dev/sandbox/b]
[meta.2, /Users/mribeirodantas/dev/sandbox/a2]
[meta.2, /Users/mribeirodantas/dev/sandbox/b2]
[meta.2, /Users/mribeirodantas/dev/sandbox/c]
[meta.3, /Users/mribeirodantas/dev/sandbox/a3]