Subset/shuffle

sort: Sort records by sequence or any other criterion
unique: De-replicate by sequence and/or other properties, returning only unique records
filter: Keep/exclude sequences based on different properties with a mathematical (JavaScript) expression
split: Distribute sequences into multiple files based on a variable/function or advanced expression
sample: Get a random subset of sequences; either a fixed number or an approximate fraction of the input
slice: Return a range of sequence records from the input
head: Return the first N sequences
tail: Return the last N sequences
interleave: Interleave records of all files in the input