esl-selectn

name	esl-selectn
description	Use when reservoir-sampling a fixed number of random lines from a large text file or stream without loading the whole file.
disable-model-invocation	true
user-invocable	true

esl-selectn

Quick Start

• Command: esl-selectn [-options] <n> <file>
• Local executable: /home/vimalinx/miniforge3/envs/bio/bin/esl-selectn
• Extended help: See references/help.md

When To Use This Tool

• Use esl-selectn when the thing you want to sample is one physical line per record.
• It is useful for downsampling huge ID lists, score tables, one-record-per-line exports, or stdin streams in a single pass.
• Reach for --seed when you need the same sampled subset on repeated runs.

Common Patterns

# Sample 100 random lines from a text file
esl-selectn 100 all-records.txt > sample.txt

# Reproducible sampling with a fixed seed
esl-selectn --seed 42 500 ids.txt > ids.sample.txt

# Sample directly from a stream
cat metrics.tsv | esl-selectn 1000 - > metrics.sample.tsv

Recommended Workflow

1. Make sure each logical record you care about is represented by exactly one line.
2. Choose the sample size n and whether you need reproducibility.
3. Run esl-selectn on the file or stream, redirecting stdout to the sampled output.
4. Validate the sampled line count and spot-check that the input format survived intact.

Guardrails

• This tool samples lines, not FASTA, FASTQ, or Stockholm records. Multi-line biological records must be flattened or sampled by another method first.
• The implementation is single-pass reservoir sampling, so memory scales with n, not with full file size.
• -h works; --help and --version are rejected by the local executable.
• file may be - to read from stdin.