r - data.table fast acces to column by expression -


i trying column data.table given expression. receive caseid expression. expr_caseid <- expression(caseid). how column expression in fastest possible way?

library(data.table) dt_fcst <- data.table(caseid = as.integer(runif(1e8)*100))  expr_caseid <- expression(caseid)  testexpr = function(dt_, expr_){     dt_[[deparse(substitute(expr_))]] }  testgetelement = function(dt_, expr_){     getelement(dt_, deparse(substitute(expr_))) }  library(microbenchmark) microbenchmark( ##  by_char = dt_fcst[['caseid']],     by_deparse = testexpr(dt_fcst, caseid), ##  by_expr = dt_fcst[, list(caseid)], ##  by_dollar = dt_fcst$caseid,     by_eval = eval(         expr_caseid,          envir = as.environment(dt_fcst)     ),     by_getelement = testgetelement(dt_fcst, caseid) #   ,by_index = dt_fcst@.data[[1]] , times = 1000l)

results of performance measurements:

unit: microseconds

          expr  min    lq    mean median   uq   max neval cld     by_deparse 37.2 41.35 55.0700  46.15 60.6 357.8  1000   b        by_eval 15.9 22.30 29.2194  24.80 34.3 289.8  1000    by_getelement 38.3 42.20 55.9087  47.30 63.2 283.3  1000   b

with comment frank

unit: microseconds             expr  min    lq     mean median    uq     max neval cld  by_evalnocoerce  1.8  4.00   8.7652   5.30  7.60   479.8  1000     microbenchmark( ##  by_char = dt_fcst[['caseid']],     by_deparse = testexpr(dt_fcst, caseid), ##  by_expr = dt_fcst[, list(caseid)], ##  by_dollar = dt_fcst$caseid,     by_eval = eval(         expr_caseid,          envir = as.environment(dt_fcst)     ),     by_getelement = testgetelement(dt_fcst, caseid),     by_evalnocoerce = eval(expr_caseid, dt_fcst) #   ,by_index = dt_fcst@.data[[1]] , times = 1000l)

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