What's the difference between using select + unlist from dplyr package and using the dollar sign?

Question

I've been taking an online course in which the instructor always does the following to obtain, say, the column Col1 from a data.frame object Dat:

library(dplyr)
unlist(select(Dat, Col1))

Why not simply run Dat$Col1? I notice a difference in the "presentation" of both results, but is there any other significant divergence between the two forms? Any operation will result in the same product for both?

Answer 1

(Posting comments as community wiki.)

These are not quite equivalent - unlist(select(.)) keeps (probably unwanted) names.

dd <- data.frame(Col1=c("abc","def"))
str(unlist(select(dd,Col1)))
##  Factor w/ 2 levels "abc","def": 1 2
##  - attr(*, "names")= chr [1:2] "Col11" "Col12"
str(dd$Col1)
##  Factor w/ 2 levels "abc","def": 1 2

Your instructor is probably just a fan of the tidyverse (@RichScriven); pull(Dat, Col1) or (for extreme "tidiness") Dat %>% pull(Col1) would be more idiomatic (@Henrik). Dat$Col1 or Dat[["Col1"]] would be the base-R equivalents (the former is more convenient for interactive use, the latter is marginally safer for programming purposes since it won't do name-completion).

It hardly matters, but the tidyverse approaches are much slower.

microbenchmark(dd$Col1,dd[["Col1"]],pull(dd,Col1),unlist(select(dd,Col1)))
Unit: microseconds
                     expr     min        lq       mean    median       uq
                  dd$Col1   5.296   10.9630   14.86871   13.4040   17.160
             dd[["Col1"]]   7.870    9.6535   15.18874   11.8270   16.635
           pull(dd, Col1)  44.160  108.7625  128.89342  117.8415  136.890
 unlist(select(dd, Col1)) 601.480 1132.8240 1436.44178 1214.4420 1378.141
      max neval cld
   31.036   100  a 
   88.842   100  a 
  422.462   100  a 
 8796.964   100   b