a seeded sample not working properly when an index is present

[jqnatividad]

I have a somewhat sparse tsv file with 45m rows, 24 columns - about 4.3 gb.

When I run xsv sample --seed 42 1000 file.tsv -o output.csv without an index, it takes about 15 seconds and produces a reproducible sample.

However, when I create an index (xsv index file.tsv - takes about 12 seconds, producing a 350mb IDX file), and run a sample using the same seed, it is fast (2 seconds), but produces a different sample for each run, as if I didn't specify a seed.

[jqnatividad]

After looking at the code, this partially explains the issue

xsv/src/cmd/sample.rs

Lines 17 to 19 in 3de6c04

	When an index is present, this command will use random indexing if the sample
	size is less than 10% of the total number of records. This allows for efficient
	sampling such that the entire CSV file is not parsed.

basically, short circuiting the seed parameter.

I ran a bigger sample( more than 10% ) using the same tsv file (xsv sample --seed 42 5000000 file.tsv -o output2.csv), and I can confirm its now reproducible, with and without an index.

However, why does it ignore the seed parameter only when an index is present when the sample size is less than 10%? Shouldn't seed always takes precedence over the <10% sample size check?