r - data.table assignment by reference within function -

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this question has answer here:

i have (big-ish) data.table. , want same thing many of columns. say,

dt <- data.table( ltr = letters[1:5] ) func <- function( dt ){     cols <- colnames( dt ) # columns apply op     dt[ , (cols) := lapply( .sd, toupper ), .sdcols = cols ]     return( dt ) }

the function func converts characters upper case columns. try

func( dt )

i error

error in `:=`((cols), lapply(.sd, toupper)) :  check is.data.table(dt) == true. otherwise, := , `:=`(...) defined use in j, once , in particular ways. see help(":=").

i'm still not sure causes error , have read help(":="), faqs , other (so) sources. help?

note: should have given more details context. func function written in package. makes difference

the short answer make sure package data.table aware. see @arun's comment.

note using devtools::use_package( "data.table", pkg = "." ) add imports field in description not explicitly import( data.table ) in namespace. such, including data.table in depends field -- that's first option matthew outlines in post -- may more foolproof.


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