I try to write a simple function wrapping around the dplyr::case_when() function. I read the programming with dplyr documentation on https://cran.r-project.org/web/packages/dplyr/vignettes/programming.html but can't figure out how this works with the case_when() function.
I have the following data:
data <- tibble(
item_name = c("apple", "bmw", "bmw")
)
And the following list:
cat <- list(
item_name == "apple" ~ "fruit",
item_name == "bmw" ~ "car"
)
Then I would like to write a function like:
category_fn <- function(df, ...){
cat1 <- quos(...)
df %>%
mutate(category = case_when((!!!cat1)))
}
Unfortunately category_fn(data,cat)
gives an evaluation error in this case. I would like to obtain the same output as the output obtained by:
data %>%
mutate(category = case_when(item_name == "apple" ~ "fruit",
item_name == "bmw" ~ "car"))
What is the way to do this?
Here's another tidyverse centric approach
cat <- tribble(
~name, ~category,
"apple", "fruit",
"bmw", "car"
) %>%
str_glue_data("item_name == '{name}' ~ '{category}'")
data %>%
mutate(category = case_when(!!! map(cat, rlang::parse_expr)))
Quote each element of your list first:
cat <- list(
quo(item_name == "apple" ~ "fruit"),
quo(item_name == "bmw" ~ "car")
)
Your function does not then have to quote the cat object itself. I have also changed the use of the "everything else" ... argument to refer to the category argument explicitly in the call:
category_fn <- function(df, categories){
df %>%
mutate(category = case_when(!!!categories))
}
The output of the function is then as expected:
category_fn(data, cat)
# A tibble: 3 x 2
item_name category
<chr> <chr>
1 apple fruit
2 bmw car
3 bmw car
For completeness, I note that the category list works with your function when defined using the base R quote() function too:
cat <- list(
quote(item_name == "apple" ~ "fruit"),
quote(item_name == "bmw" ~ "car")
)
> cat
[[1]]
item_name == "apple" ~ "fruit"
[[2]]
item_name == "bmw" ~ "car"
> category_fn(data, cat)
# A tibble: 3 x 2
item_name category
<chr> <chr>
1 apple fruit
2 bmw car
3 bmw car
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