More on Macros in R

February 23, 2019
By

(This article was first published on R – Win-Vector Blog, and kindly contributed to R-bloggers)

Recently ran into something interesting in the R macros/quasi-quotation/substitution/syntax front:

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Romain François: “[email protected]_lionelhenry reveals planned double curly syntax At #satRdayParis as a possible replacement, addition to !! and enquo()”

It appears !! is no longer the last word in substitution (it certainly wasn’t the first).

The described effect is actually already pretty easy to achieve in R.

suppressPackageStartupMessages(library("dplyr"))

group_by <- wrapr::bquote_function(group_by)
summarize <- wrapr::bquote_function(summarize)

my_average <- function(data, grp_var, avg_var) {
  data %>%
    group_by(.( grp_var )) %>%
    summarize(avg = mean(.( avg_var ), na.rm = TRUE))
}

data <- data.frame(x = 1:10, g = rep(c(0,1), 5))

my_average(data, as.name("g"), as.name("x"))

## # A tibble: 2 x 2
##       g   avg
##    
## 1     0     5
## 2     1     6

Or if you don’t want to perform the quoting by hand.

my_average <- function(data, grp_var, avg_var,
                       grp_var_name = substitute(grp_var),
                       avg_var_name = substitute(avg_var)
                       ) {
  data %>%
    group_by(.( grp_var_name )) %>%
    summarize(avg = mean(.( avg_var_name ), na.rm = TRUE))
}

my_average(data, g, x)

## # A tibble: 2 x 2
##       g   avg
##    
## 1     0     5
## 2     1     6

And we can use the same Thomas Lumley / bquote() notation for string interpolation.

group_var <- as.name("g")
avg_var <- as.name("x")

wrapr::sinterp("group_var was .(group_var), and avg_var was .(avg_var)")

# [1] "group_var was g, and avg_var was x"

The .() notation has a great history in R and has been used by data.table for years.

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