Tidy evaluation, most common actions
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Tidy evaluation is a bit challenging to get your head around. Even after reading programming with dplyr several times, I still struggle when creating functions from time to time. I made a small summary of the most common actions I perform, so I don’t have to dig in the vignettes and on stackoverflow over and over. Each is accompanied with a minimal example on how to implement it. I thought others might find this useful too, so here it is in a blog post. This list is meant to be a living thing so additions and improvements are most welcome. Please do a PR on this file or send an email.
library(tidyverse)
bare to quosure: quo
bare_to_quo <- function(x, var){
x %>% select(!!var) %>% head(1)
}
bare_to_quo(mtcars, quo(cyl))
## cyl
## Mazda RX4 6
bare to quosure in function: enquo
bare_to_quo_in_func <- function(x, var) {
var_enq <- enquo(var)
x %>% select(!!var_enq) %>% head(1)
}
bare_to_quo_in_func(mtcars, mpg)
## mpg
## Mazda RX4 21
quosure to a name: quo_name
bare_to_name <- function(x, nm) {
nm_name <- quo_name(nm)
x %>% mutate(!!nm_name := 42) %>% head(1) %>%
select(!!nm)
}
bare_to_name(mtcars, quo(this_is_42))
## this_is_42
## 1 42
quosure to text: quo_text
quo_to_text <- function(x, var) {
var_enq <- enquo(var)
ggplot(x, aes_string(rlang::quo_text(var_enq))) + geom_density()
}
plt <- quo_to_text(mtcars, cyl)
Note that tidy evaluation is not yet implemented in ggplot2, but this will be in future versions. This is a workaround for the meantime, when combining dplyr and ggplot2.
character to quosure: sym
char_to_quo <- function(x, var) {
var_enq <- rlang::sym(var)
x %>% select(!!var_enq) %>% head(1)
}
char_to_quo(mtcars, "vs")
## vs
## Mazda RX4 0
multiple bares to quosure: quos
bare_to_quo_mult <- function(x, ...) {
grouping <- quos(...)
x %>% group_by(!!!grouping) %>% summarise(nr = n())
}
bare_to_quo_mult(mtcars, vs, cyl)
## # A tibble: 5 x 3
## # Groups: vs [?]
## vs cyl nr
## <dbl> <dbl> <int>
## 1 0 4 1
## 2 0 6 3
## 3 0 8 14
## 4 1 4 10
## 5 1 6 4
multiple characters to quosure: syms
bare_to_quo_mult_chars <- function(x, ...) {
grouping <- rlang::syms(...)
x %>% group_by(!!!grouping) %>% summarise(nr = n())
}
bare_to_quo_mult_chars(mtcars, list("vs", "cyl"))
## # A tibble: 5 x 3
## # Groups: vs [?]
## vs cyl nr
## <dbl> <dbl> <int>
## 1 0 4 1
## 2 0 6 3
## 3 0 8 14
## 4 1 4 10
## 5 1 6 4
quoting full expressions
Altough quoting column names is most often used, it is by no means the only option. We can use the above to quote full expressions.
filter_func <- function(x, filter_exp) {
filter_exp_enq <- enquo(filter_exp)
x %>% filter(!!filter_exp_enq)
}
filter_func(mtcars, hp == 93)
## mpg cyl disp hp drat wt qsec vs am gear carb
## 1 22.8 4 108 93 3.85 2.32 18.61 1 1 4 1
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