using character vector as input argument to setkey (data.table pakcage)

[Sean Zhang]

Dear R helpers,

I wonder how to use a character vector as an input argument to setkey
(data.table package).
The following works:

library(data.table)
test.dt <- data.table(expand.grid(a=1:30,b=LETTERS),c=seq(30*26))
setkey(test.dt,a,b)

I like a similar function, but can accept c('a','b') as an input argument as
below
setkey.wanted(test.dt,c('a','b'))

Your help will be highly appreciated.

-Sean

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