iacobus - 6 months ago 46

R Question

I'm working on a function that takes an argument

`funs`

`vars`

`summarize_at`

`funs`

This works with the functions that are built-in R but doesn't seem to work with user-defined functions. It reports an error that it can't find the user-defined function. However,

`summarize_at`

This function is part of a larger function that produces a box for a Shiny Dashboard. I'd prefer not to have (and have to maintain) a different Shiny module for each type of box (each function and function argument combination).

A minimal reproducible example is below:

`# function to compute summary stat`

compute_box_value <- function(data, vars, funs) {

f = funs_(funs)

result <- data %>%

summarize_at(.cols = vars, .funs = f)

}

# simple user defined function that gets count of rows with certain values of x

equals <- function(x, test_value) {

sum(x %in% test_value)

}

x <- data.frame(value = sample(1:5, 10, TRUE))

vars <- c("value")

# this works

print(compute_box_value(x, vars, "mean(., na.rm = TRUE)"))

# this works

summarize_at(x, vars, .funs = "equals", test_value = 1)

# this doesn't work (error: couldn't find function equals)

print(compute_box_value(x, vars, "equals(., test_value = 1)"))

Answer

You need to use the formula (`~`

) instead of string:

```
print(compute_box_value(x, vars, ~equals(., test_value = 1)))
```

Which gives:

```
# value
#1 3
```

From the documentation:

Itâ€™s best to use a formula because a

formula captures both the expression to evaluate and the environment where the evaluation occurs. This is important if the expression is a mixture of variables in a data frame and objects in the local environment: