R/multi_merge.R

In ClaraMarquardt/ehR: A collection of R functions designed to facilitate the interaction with and analysis of EHR data.

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#' Merge together multiple data.tables. 
#' 
#' Sequentially merge a list of data.tables on a given set of variables (inner-join).
#'
#' @details Maintained by: Clara Marquardt
#'
#' @export
#' @import data.table
#' 
#' @param data_list List of data.tables which are to be merged (list - data.table).
#' @param key_var Vector of variable names on the basis of which the data.tables are to be merged (vector - character).
#' @param allow.cartesian See ?data.table (logical - TRUE/FALSE) [default: FALSE].
#' 
#' @return Merged data.table.
#' 
#' @examples
#' data_list   <- list(ed[1:100], dia[1:100], dem[1:100])
#' dt_merged <- multi_merge(data_list=data_list, key_var=c("empi"))
#' print(str(dt_merged))

multi_merge <- function(data_list, key_var, allow.cartesian=FALSE) {

  # define Reduce-based function
  multi_merge_fun <- function(x, key_var) {Reduce(function(x, y) {x[y, on=c(key_var), 
  	nomatch=0, allow.cartesian=allow.cartesian]}, x, accumulate=FALSE)}

  # apply function
  dt_merged   <- multi_merge_fun(x=data_list, key_var=key_var)

  # return
  return(dt_merged)

}



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