How to do a partial expand in Snakemake?

Question

I\'m trying to first generate 4 files, for the LETTERS x NUMS combinations, then summarize over the NUMS to obtain one file per element in LETTERS:

LETTERS =         


        

Answer 1

Partial expand is possible using allow_missing=True.

For example:

expand("text_{letter}_{num}.txt", num=NUMS, allow_missing=True)

["text_{letter}_1.txt", "text_{letter}_2.txt"]