R: group by list of column names -


i have data table result join between 2 other tables (a, b)

joinedtable   = a[b, on = columnname]

i want count frequency of rows combinations based con column names can vary (all, 1 on somewhere in middle). problem works being hardcoded not variable:

joinedtable[, list(freq =.n), = list( column_a, column_b, ...)] # works  # what's next doesn't columns = names(joinedtable)[-which(names(joinedtable) %in% c('column_f', 'column_g',...))]     joinedtable[, list(freq =.n), = as.list(columns)] # doesn't work

if try dynamic error:

error in `[.data.table`(joinedtable, , list(freq = .n), = list(outcolumns)) :    items in 'by' or 'keyby' list length (13). each must same length rows in x or number of rows returned (23).

how should works?

already found answer , it's pretty simple , silly error:

this line

joinedtable[, list(freq =.n), = as.list(columns)]

needs changed to:

joinedtable[, list(freq =.n), = columns]

since columns array.


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