R Under development (unstable) (2023-11-16 r85542 ucrt) -- "Unsuffered Consequences"
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> library("R.utils")
Loading required package: R.oo
Loading required package: R.methodsS3
R.methodsS3 v1.8.2 (2022-06-13 22:00:14 UTC) successfully loaded. See ?R.methodsS3 for help.
R.oo v1.25.0 (2022-06-12 02:20:02 UTC) successfully loaded. See ?R.oo for help.

Attaching package: 'R.oo'

The following object is masked from 'package:R.methodsS3':

    throw

The following objects are masked from 'package:methods':

    getClasses, getMethods

The following objects are masked from 'package:base':

    attach, detach, load, save

R.utils v2.12.3 successfully loaded. See ?R.utils for help.

Attaching package: 'R.utils'

The following object is masked from 'package:utils':

    timestamp

The following objects are masked from 'package:base':

    cat, commandArgs, getOption, isOpen, nullfile, parse, warnings

> 
> urls <- c(
+   "http://www.r-project.org/",
+   "ftp://cran.r-project.org/",
+   "htttp://www.r-project.org/",  ## typo, but still a URL
+   "",                            ## empty
+   NA_character_                  ## missing
+ )
> 
> print(urls)
[1] "http://www.r-project.org/"  "ftp://cran.r-project.org/" 
[3] "htttp://www.r-project.org/" ""                          
[5] NA                          
> 
> res <- sapply(urls, FUN=isUrl)
> print(res)
 http://www.r-project.org/  ftp://cran.r-project.org/ 
                      TRUE                       TRUE 
htttp://www.r-project.org/                            
                      TRUE                      FALSE 
                      <NA> 
                     FALSE 
> 
> res <- isUrl(urls)
> print(res)
[1]  TRUE  TRUE  TRUE FALSE FALSE
> stopifnot(is.logical(res))
> stopifnot(length(res) == length(urls))
> stopifnot(!any(is.na(res)))
> 
> proc.time()
   user  system elapsed 
   0.23    0.17    0.39