[SOLVED] "quiet" functions and assert condition

"quiet" functions and assert condition

I don't understand why the following stopifnot does not error out:

> suppressMessages(library(tidyverse))
> print(.packages())
 [1] "lubridate" "forcats"   "stringr"   "dplyr"     "purrr"     "readr"    
 [7] "tidyr"     "tibble"    "ggplot2"   "tidyverse" "stats"     "graphics" 
[13] "grDevices" "utils"     "datasets"  "methods"   "base"     
> stopifnot(.packages()==c())
> # The preceding stopifnot should have errored out

Solution

c() returns a NULL. .packages() == c() returns logical vector of length 0 since no comparisons performed. stopifnot function checks its arguments with all function, and apparently all(NULL) returns TRUE (none of its input is FALSE).

If you need to check if your variable is null, use is.null or is_empty function:

is.null(c())
#> [1] TRUE
is_empty(c())
#> [1] TRUE

If you want to check if all required packages are loaded use %in% operator with all function:

stopifnot(all(required_packages %in% .packages()))

or with setdiff:

length(setdiff(required_packages, .packages())) == 0