R 使用data.table列中的参数按引用更新

我有以下数据表和函数，用于提取参数并将其作为列添加到数据表中：

library(stringr)
library(data.table)

pq <- c("cm_mmc=MSN-_-Exact-_-BrandExact-_-CheddarCheese"
  ,"cm_mmc=Google-_-cheeseTypes-_-cheddar-_-cheesedelivered&gclid=CMXyy2D81MsCFcsW0w0dMVoPGw"
  ,"cm_mmc=MSN-_-worldcitiesuslocations-_-cheese-_-cheeseshops"
  ,"cm_mmc=MSN-_-worldcitiesuslocations-_-cheese-_-cheeseshops")


rq <- c("q=cheese&src=IE-SearchBox&FORM=IESR02",
                   "sa=L",
                   "q=london+cheese+shop&src=IE-TopResult&FORM=IETR02&pc=WCUG",
                   "q=london+cheese+shop&src=IE-TopResult&FORM=IETR02&pc=WCUG")

DT = data.table(page_urlquery = pq, refr_urlquery = rq)

# Extracts a paramater from the relevant query and adds it to the table as a column
extract_param <- function(dt, source = c("page_urlquery", "refr_urlquery"), param_name){
  source <- match.arg(source)
  regexp <- paste("(?i)", param_name, "=([^&]+)", sep="")
  col_name <- switch(source
                     ,"page_urlquery" = paste("url_", param_name, sep = "")
                     ,"refr_urlquery" = paste("ref_", param_name, sep = "")
  )

  dt[,(col_name):= str_match((source), regexp)[,2]]
}

---

它创建列，但内容为空。我认为数据表源参数中的语法有问题。我缺少什么？

将函数中的代码从

dt[,(col_name):= str_match((source), regexp)[,2]]

到

dt[,(col_name):= str_match((source), regexp)[,2]]

  dt[,(col_name):= str_match(get(source), regexp)[,2]]