Step 3 - Operate on a stream using a process

In the previous example, we ran 3 parallel executions each time applying the same simple function: adding one. Let us simulate now a more real-life example where parallel executions will not take the same amount of time. We do this by defining a process and workflow that uses this process. The rest is similar to our example before.

// Step - 3
process add {
  input:
    val(input)
  output:
    val(output)
  exec:
    output = input + 1
}
workflow step3 {
  Channel.from( [ 1, 2, 3 ] ) \
    | add \
    | view{ it }
}

Running it is again the same.

> nextflow -q run . -entry step3
WARN: DSL 2 IS AN EXPERIMENTAL FEATURE UNDER DEVELOPMENT -- SYNTAX MAY CHANGE IN FUTURE RELEASE
2
4
3

The result will be a permutation of 2,3 and 4. Try it multiple times to verify for yourself that the order is not guaranteed to be the same. Even though the execution times will not be that much different! In other words, a Channel does not guarantee the order, and that’s a good thing.