"Error in library(rjson): There is no package called rjson" - r

Question

My rjson package randomly doesn't work. As in, it works fine sometimes, sometimes it fails to load. Not sure why.
I get this error.
Error in library("rjson") : there is no package called ‘rjson’
To try and alleviate this, despite knowing its installed, I added an install line in my script.
install.packages("rjson", repos="http://cran.rstudio.com/")
library(rjson)
Now I get....
Installing package(s) into ‘C:/Users/Tom/Documents/R/win-library/2.15’
(as ‘lib’ is unspecified)
trying URL 'http://cran.rstudio.com/bin/windows/contrib/2.15/rjson_0.2.13.zip'
Content type 'application/zip' length 491848 bytes (480 Kb)
opened URL
downloaded 480 Kb
package ‘rjson’ successfully unpacked and MD5 sums checked
Warning: cannot remove prior installation of package ‘rjson’
The downloaded binary packages are in
C:\Users\Tom\AppData\Local\Temp\RtmpiOfTqK\downloaded_packages
In R, when I go to "Packages --> Load" for some reason rjson is NOT there. It never has been, even when it worked.
I've naviaged to...
C:\Users\Tom\Documents\R\win-library\2.15
I can confirm the folder for rjson is there.
No idea what to do.

Answer 1

This has happened to me quite a few times. It usually happens when you try to install a newer version of an already installed package (although it can happen in other more rare occasions).
The solution I have found so far is to go back to your library path i.e. the location on your machine where the package is installed (C:\Users\user_name\Documents\R\win-library\R_version is the default path on Windows) delete the corresponding package folder and then re-install the package as usual using:
install.packages('rjson')
And this way it should work.
Or you could even do it programmatically as per #Thomas 's comment:
#get list of installed packages
inst_packages <- installed.packages()
if ("rjson" %in% inst_packages[, 1]) {
#uninstalls package
remove.packages("rjson")
#re-installs package
install.packages("rjson")
}
or even better just use:
if ("rjson" %in% inst_packages[, 1]) update.packages("rjson")