nextflow-io/nextflow

Expand `.splitCsv()` to allow comments in CSV and TSV files

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#6705 opened on Jan 8, 2026

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 (6 comments) (1 reaction) (0 assignees)Groovy (3,382 stars) (784 forks)batch import
good first issue

Description

New feature

Someone opened a feature request on nf-schema to ask to allow comments (#) in CSV and TSV files. I however think this would be an awesome upstream addition to the .splitCsv() method so everyone can benefit from that feature. Comments syntax as explained here makes the most sense I think: https://www.w3schools.io/file/csv-comments/

Use case

Easier debugging in CSV and TSV files by allowing directly commenting out lines in those files. This could also help to add some comments and explanation to those files without breaking them.

Suggested implementation

I think this should not be default behaviour of the function but adding an option like comments:true would be an ideal solution IMO

Thanks!

Contributor guide

Tech stack
None
Domain
backenddata
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Groovy basicsNextflow DSLCSV formatUnit testing
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
Investigate the current implementation of `.splitCsv()` in the Nextflow codebase, likely located in the `nextflow.script` package. The new `comments` option should be added as an optional parameter. Look at how other options are handled in similar operators for consistency. Additionally, review the linked feature request (https://github.com/nextflow io/nf schema/issues/193) for additional context on expected comment syntax.