Convert sc-matrix to simulated bulk
as_bulk(m, groups = NULL, isLog = TRUE, by = "mean")non-row-centered logTPM or TPM matrix.
if not NULL, return a simulated bulk column per group in groups. Default: NULL
set to FALSE if 'm' is in TPM form. Default: TRUE
simulated bulk matrix. If groups is NULL, one column is returned for the average across all cells. Else one column per group in 'groups'.