No. of discarded cells do not add up?

[shaln]

Hello,

I have a question about the number of cells to be discarded identified using the code below.

qc.stats2 <- perCellQCFilters(per.cell, 
    sub.fields=c("subsets_Mito_percent", "altexps_ERCC_percent")) 
colSums(as.matrix(qc.stats2))

##              low_lib_size            low_n_features high_subsets_Mito_percent 
##                         0                         3                       128 
## high_altexps_ERCC_percent                   discard 
##                        65                       189

The total number of cells to discard (189) does not match the sum of 3 + 128 + 65 = 193. Am I misunderstanding the output here?

Thank you.

[PeteHaitch]

Cells may be discarded for multiple reasons, e.g., a cell may be present in both the low_n_features and high_subsets_Mito_percent sets.