group comparison - mRNA tab does not work when comparing a single sample group to another group

[MatthijsPon]

When comparing a single sample to another group w/ group comparison, the mRNA tab shows 'No data to plot'. However, when comparing a group of 2 samples to the same group, the tab does work.

• If this is not intended, my guess would be that this might have something to do with the statistical calculations in the backend? The fetch for mRNA returns an empty list (/api/expression-enrichments/fetch?enrichmentType=SAMPLE).
• If this is intended, perhaps we could set an error message stating that single samples cannot be compared on the mRNA level so that this is more clear to users?

Reproduce: Sample 1 vs all except 1+2: Does not work sample 2 vs all except 1+2: Does not work

Sample 1+2 vs all except 1+2: Works

Sample 1 vs Sample 2 vs all except 1+2: Does not work

[MatthijsPon]

@alisman I cannot add this to the sprint

[alisman]

@MatthijsPon, @jjgao says the following:

It is not meaningful to perform a t-test when one group only has a single sample. This is also how it’s coded in the java lib we are using: http://home.apache.org/~luc/commons-math-3.6-RC2-site/jacoco/org.apache.commons.math3.stat.inference/TTest.java.html

So, I think the resolution here is as you suggest, to improve the message. @jjgao suggests:

That could work, something like - “this analysis requires that each group has 2 or more samples to compare”

I can take care of this.

[MatthijsPon]

Alright, that is very logical. Thanks for helping with this @alisman!