How to select rows in a table whose row.names match any element from a character vector?

Question

I have a big table (over 20,000 rows) containing a couple of columns saved in a matrix x. I also have character vector z containing a couple of thousand of the row names used in the big table. How can I extract all the rows from the matrix x where the row name matches one of elements in the vector z?

Answer 1

x[row.names(x) %in% z, ]

Will work if x has a row.names attribute, like a dataframe. You used the words data table and array, so I'm not certain of your exact data structure.