Define more (and more flexible) stacks #117
Description
Making a data-data or MC-MC comparison plot requires some hacking of the config file (see #112), and signals are not stacked (nor combined for different eras, see #115).
Currently, the division is done by looking at the "type" of the sample/file:
- "data" is added to the data stack (as-is, no scaling or normalisation, unless the plot is normalised)
- "MC" is scaled to luminosity times cross-section divided by the sum of weights (times "scale"), unless "no-lumi-rescaling" is true, and added to the MC stack
- "signal" is scaled like MC, but not added to a stack.
How about allowing a "stack" property that is the type by default (for "data" and "MC", and the "pretty-name" by for signal), that can also be set per sample (per group?).
Possibly this could also allow for overlaying several ratio plots.
Maybe this is too complicated, and it would be better to have a simple python implementation that does not use eras or stacks for this (the typical use case is comparing a few MC samples with different settings, but there are also more analysis-like cases that could benefit from it)?