Bootstrapping replicates...
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Error in `[.data.table`(Transcripts, , `:=`(sumB, rowSums(counts_B, na.rm = TRUE))) : 
RHS of assignment to existing column 'sumB' is zero length but not NULL. 
If you intend to delete the column use NULL. 
Otherwise, the RHS must have length > 0; e.g., NA_integer_. 
If you are trying to change the column type to be an empty list column then, 
as with all column type changes, provide a full length RHS vector such as 
vector('list',nrow(DT)); i.e., 'plonk' in the new column.