R – Select columns of data.table based on regex


How can I select columns of a data.table based on a regex?
Consider a simple example as follows:

mydt <- data.table(foo=c(1,2), bar=c(2,3), baz=c(3,4))

Is there a way to use columns of bar and baz from the datatable based on a regex? I know that the following solution works but if the table is much bigger and I would like to choose more variables this could easily get cumbersome.

mydt[, .(bar, baz)]

I would like to have something like matches() in dplyr::select() but only by reference.

Best Solution

You can also try to use %like% from data.table package, which is a "convenience function for calling regexpr". However makes code more readable ;)

In this case, answering your question:

mydt[, .SD, .SDcols = names(mydt) %like% "bar|baz"]

As %like% returns a logical vector, whe can use the following to get every column except those which contain "foo":

mydt[, .SD, .SDcols = ! names(mydt) %like% "foo"]

where !negates the logical vector.