Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.
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
R-bloggers.com offers daily e-mail updates about R news and tutorials about learning R and many other topics. Click here if you're looking to post or find an R/data-science job.
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.