Composing strings based on multiple conditions

Tips & Tricks
1

When composing longer strings based on multiple tests in Nextflow workflows, using the ternary operator or string concatenation can lead to long, hard-to-read lines of code. An alternative approach is to use a list to store the parts and then join them to create the final string. This method improves readability and maintainability.

e.g.

ext.args = {"-ax ${meta.readtype.equals("hifi") ? "map-hifi" : meta.readtype.equals("clr") ? "map-pb" : meta.readtype.equals("ont") ? "map-ont" : meta.readtype.equals("illumina") ? "sr" : ""} --cs=short ${reference.size() > 2.5e9 ? (" -I" + Math.ceil(reference.size()/1e9)+"G") : ""}" }

could become

        ext.args = { [
            meta.read_type.equals("hifi") ? "-ax map-hifi" : "",
            meta.read_type.equals("clr") ? "-ax map-pb" : "",
            meta.read_type.equals("ont") ? "-ax map-ont" :"",
            meta.read_type.equals("illumina") ? "-ax sr" : "",
            "--cs=short",
            reference.size() > 2.5e9 ? (" -I" + Math.ceil(reference.size()/1e9)+"G") : "",
        ].minus("").join(" ") }

Key improvements:

  • Each condition is on a new line, which improves readability.
  • The .minus("") removes all empty strings (an alternative is .findAll() which removes anything that evaluates to Groovy false - [ [], 0, "", '', false ] ).
  • Then join(" ") which combines the remaining parts with spaces.

This improves maintainability, as adding and removing conditions becomes easier.

( Written with the aid of Seqera AI )

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