Use ddply within a function and include variable of interest as an argument

Question

I am relatively new to R, and trying to use ddply & summarise from the plyr package. This post almost, but not quite, answers my question. I could use some additional ex

Answer 1

With the introduction of quosures in the devel version of dplyr (soon to be released 0.6.0), this becomes a bit more easier

library(dplyr)
descriptives_by_groupN <- function(dataset, group, x) {

   group <- enquo(group)
   x <- enquo(x)

  dataset %>%
         group_by(!!group) %>%
         summarise(Mean = mean(!!x),
                SD = sd(!!x),
                Min = min(!!x),
                Max = max(!!x))
}

descriptives_by_groupN(mtcars, cyl, hp)
# A tibble: 3 × 5
#   cyl      Mean       SD   Min   Max
#             
#1     4  82.63636 20.93453    52   113
#2     6 122.28571 24.26049   105   175
#3     8 209.21429 50.97689   150   335

Here, the input arguments are converted to quosures with enquo, and inside the group_by/summarise, unquote the quosures (!! or UQ) to get it evaluated