Discard taxa with less than the given minimum number of occurrences.
filterTaxonMatrix( x, minocc = 0, keepSum = FALSE, return.filtered.indices = FALSE )
taxon abundance matrix, rows are taxa, columns are samples
minimum occurrence (minimum number of samples with non-zero taxon abundance)
If keepSum is true, the discarded rows are summed and the sum is added as a row with name: summed-nonfeat-rows
if true, return an object with the filtered abundance matrix in mat and the indices of removed taxa in the original matrix in filtered.indices
filtered abundance matrix