data.table: using setkey with a column name variable

21
votes

I have a variable name saved into the string variable which_id.

W is a data.table. How do I call setkey on W with which_id ?

This is what I've tried

 > eval( paste( 'setkey(W,' , which_id , ')' ) )
[1] "setkey(W, customer_id_A )"

But a call to tables() shows that the 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?

1
rdata.table
I don't think the fancy eval stuff will be needed. Your last try, with setkeyv should work, I think. Anyway, the way I usually do evals is with eval(parse(text="...")) whereas you are doing eval("..."). - Frank
The parse call did the trick, thanks. I was wondering if there was a 'data.table-native' way. - user2105469
setkeyv(W, which_id) works for me, you may want to make your question reproducible - put in specific W and which_id - eddi

1 Answers

23
votes

setkeyv should work. Here is a 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