I am trying to get a column from data.table by given expression. I receive CaseID
as an expression. expr_caseid <- expression(CaseID)
. How do I get the column by expression in a 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$CaseID,
by_eval = eval(
expr_caseid,
envir = as.environment(dt_fcst)
),
by_getElement = testGetElement(dt_fcst, CaseID)
# ,by_index = dt_fcst@.Data[[1]]
, times = 1000L)
Results of performance measurements:
Unit: microseconds
expr min lq mean median uq max neval cld
by_deparse 37.2 41.35 55.0700 46.15 60.6 357.8 1000 b
by_eval 15.9 22.30 29.2194 24.80 34.3 289.8 1000 a
by_getElement 38.3 42.20 55.9087 47.30 63.2 283.3 1000 b
with comment by Frank
Unit: microseconds
expr min lq mean median uq max neval cld
by_evalNoCoerce 1.8 4.00 8.7652 5.30 7.60 479.8 1000 a
microbenchmark(
## by_char = dt_fcst[['CaseID']],
by_deparse = testExpr(dt_fcst, CaseID),
## by_expr = dt_fcst[, list(CaseID)],
## by_dollar = dt_fcst$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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