r - data.table: using setkey with a column name variable -

i have variable name saved string variable which_id.

w data.table. how call setkey on w which_id ?

this i've tried

 > eval( paste( 'setkey(w,' , which_id , ')' ) ) [1] "setkey(w, customer_id_a )" 

but call tables() shows customer_id_a key didn't take.

 > evalq( paste( 'setkey(w,' , which_id , ')' ) ) [1] "setkey(w, customer_id_a )" 

customer_id_a key still didn't take.

 > setkeyv( w , cols=which_id ) 

and

 > setkeyv( w , cols=c( which_id ) ) 

--> same thing, customer_id_a key isn't there.

any pointers? thanks.

setkeyv should work. here reproducible example:

library(data.table) w <- data.table(customer_id_a = 1:2) which_id <- "customer_id_a" setkeyv(w, which_id) tables() ##      name nrow mb cols          key           ## [1,] w       2 1  customer_id_a customer_id_a ## total: 1mb