This function create a contrast matrix to be used by limma.
Arguments
- targets
A n*2 dataframe, where n is the number of samples. First column correspond to samples, second column correspond to conditions.
- comparisons
a list of numeric vectors. Each vector represent which condition should be conpared. Example : c(2,-1) means that the first condition should be substracted from second condition. Vectors can be more than two element for complex contrasts.