R/join_cols.R

In matthiaskaeding/Kaeding: What the package does (short line)

#' join_cols
#'
#' Add columns from data.table A to data.table B
#' @param A data.table receiving new columns.
#' @param B data.table providing new columns.
#' @param on Specifies the on argument for joining.
#' @param ... Other arguments passed on to ".[]"
#' @param B data.table providing new columns.
#' @keywords data.table
join_cols <- function(A,B,vars,on,...){
  
  # Build update expression.
  lhs <- vars
  rhs <- paste0("i.",lhs)
  
  inner <- paste0(lhs,"=",rhs,collapse=",")
  expr_string <- sprintf("':='(%s)",inner)
  expr <- parse(text=expr_string)
  A[B,eval(expr),on=on,...]
  
}