how to get the number of elements in Channel.fromPath or Channel.fromFilePairs

[ChenDepp]

hello everyone
how to get the number of elements in Channel.fromPath or Channel.fromFilePairs.
I want to obtain sample data and make subsequent logical judgments.
waiting for your reply
thanks

[bentsherman]

Use the count operator:

Channel.fromPath( '*.fastq' ).count().view { n -> "number of elements: ${n}" }

[ChenDepp]

the operator count I know it,but I want assign it to variable. This way I can use if else structure

[bentsherman]

Using channels in if-else statements is not supported right now, though we are looking into it. For now you will need to use operators like map, subscribe, view, etc to use the count:

Channel.fromPath( '*.fastq' ).count().map { n ->
  if( n > 0 ) {
    // ...
  }
  else {
    // ...
  }
}