detach specific package in R if loaded

Question

I'm facing some plyr vs. dplyr problems in my code, so I would like to detach the plyr packge in case it has been loaded before.

This is how far I got,

ifelse(sum(grepl("package:plyr",search()))==0,
       "plyr not loaded",
       detach("package:plyr"))

but this code throws an

Error in ifelse(sum(grepl("package:plyr", search())) == 0, 
"plyr not    loaded",  : 
substitution has length 0 
Additional warning:
In rep(no, length.out = length(ans)) :
'x' is NULL so the result will be NULL

Answer 1

Here's a solution:

if(any(grepl("package:plyr", search()))) detach("package:plyr") else message("plyr not loaded")
## plyr not loaded
library("plyr")
## if(any(grepl("package:plyr", search()))) detach("package:plyr") else message("plyr not loaded")

Generally you want to use if and else for program control and ifelse() only for vectorized logical operations, like data recoding.