How to unpack a channel that is a tuple with a key and a list

[rossijulieta]

Hi there,
I'm new to nextflow and groovy, so this may be a silly question. So the problem is I have a channel created like this:

index_ch.concat(cloud_ch)
   .map { file ->
        def key = file.name.toString().tokenize('_').get(1)
        return tuple(key, file)
     }
    .groupTuple()
    .set{ dates_ch }

and for example, dates_ch looks like this:

[20200609T002059, [/media/data/nxf/6a/9b53eb25d13d61b3f0f9c3a50fccdd/T55HCA_20200609T002059_WI_10m.tif, /media/data/nxf/a8/6c7d34e5c407173fea285061d54df3/T55HCA_
20200609T002059_S2B_FMASK_CLOUDS_10m.tif]]                                                                                                                       
[20200604T002101, [/media/data/nxf/08/507fa46db2a46065fec36ead89d309/T55HCA_20200604T002101_WI_10m.tif, /media/data/nxf/35/1138e3de09de56072f3309a13d63dd/T55HCA_
20200604T002101_S2A_FMASK_CLOUDS_10m.tif]]

and then I need to process each date and get the date two files.

process foo {
    input:
      set date, [file(a), file(b)] from dates_ch

which obviously doesn't work. Could someone let me know what the right way of declaring the input would be?

[rossijulieta]

Ok, I think I found a way around it; in case it is useful to someone else, the trick was to create channels with the date as a key and the filenames as values for the two inputs and then use join to synchronize them using the key. Like:

out_a_ch.map { file -> tuple(file.name.toString().tokenize('_').get(1), file) }
          .set{ out_a_ch_tuple }

out_b_ch.map { file -> tuple(file.name.toString().tokenize('_').get(1), file) }
          .set{ out_b_ch_tuple }

foo_in_ch = out_a_ch_tuple.join(out_b_ch_tuple)


process foo {
    input:
      set date, file(WI), file(WM) from water_in_ch

[mawasak]

Hi,
Multiple assignment should work.
Something like:

index_ch.concat(cloud_ch)
   .map { file ->
        println "FILE: $file"
        def key = file.name.toString().tokenize('_').get(1)
        return tuple(key, file)
     }
    .groupTuple()
    .set{ dates_ch }

process foo {
 input:
   tuple val(date), val(fileAB) from dates_ch

script:
def (fileAS, fileBS) = fileAB
def fileA = file(fileAS)
def fileB = file(fileBS)
//OR
// def (fileA, fileB) = [file(fileAB[0]), file(fileAB[1])]

 
 println "- $date - $fileA - $fileB"
 """
  printf '$date - $fileA -- $fileB '
 """
}

[rossijulieta]

many thanks @mawasak :)