Check if an R package is installed and if not then install it

[Ayala Allon]

Hi all,

I wanted to create a few lines of code that check if an R package is installed and if not then install it. I looked in stackoverflow and I found these great options:

http://stackoverflow.com/questions/9341635/how-can-i-check-for-installed-r-packages-before-running-install-packages

I picked to following option:

#will install the pROC library if you don't have it

if(!is.element('pROC', installed.packages()[,1]))

  {install.packages('pROC')

}else {print("pROC library already installed")}

 

And this is what I wrote:

# will install package if you don't have it

packList<- list('reshape2','psych')

for (i in 1 : length(packList)){

    if(!is.element(packList[i], installed.packages()[,1])){

        install.packages(pacList[i])

    } else {

        print(paste("###",packList[i],"package is already installed ###"), quote = FALSE)

        print(paste("### loading",packList[i], "###"),quote = FALSE)

        library(packList[i], character.only = TRUE)

    }

}

The problem is that sometime It works and sometime I get the following error:

> packList<- list('reshape2','psych')

> for (i in 1 : length(packList)){

+     if(!is.element(packList[i], installed.packages()[,1])){

+         install.packages(pacList[i])

+     } else {

+         print(paste("###",packList[i],"package is already installed ###"), quote = FALSE) 

+         print(paste("### loading",packList[i], "###"),quote = FALSE)

+         library(packList[i], character.only = TRUE)

+     }

+ }

[1] ### reshape2 package is already installed ###

[1] ### loading reshape2 ###

 Show Traceback

 Rerun with Debug

Error in as.name(pkg) : 

  invalid type/length (symbol/1) in vector allocation

 

I tried to isolate the problem and I think the problem is in:

+         library(packList[i], character.only = TRUE)

However I still cannot figure out why I occasionally get this error and how to fix it.

Any help will be greatly appreciated.

Best,

Ayala

[Tal Galili]

Hi Ayala,

Not an answer to your question, but - As an alternative approach - you can use the require2 function:

require2 <- function(package, ask= TRUE, ...) {
	package <- as.character(substitute(package))
	if(!suppressWarnings(require(package=package, character.only = TRUE))) {
	if(ask) {
	install_package <- ask.user.yn.question(paste("Package ",package,
	" is not installed. Do you want to install it now?"))
	} else {
	install_package <- TRUE
	}
	if(install_package) install.packages(pkgs=package)
	}
	require(package=package, character.only = TRUE)
	}

It tries to load a package, and if it fails in doing so, it will ask the user to install it for him.

(I include this function in the installr package:

https://github.com/talgalili/installr/blob/master/R/install.R

)

Hope this helps.

Tal

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[Ayala Allon]

Hi Tal,

Thanks!

The require2 function also loads the package after installing/ checking that I have it?

Ayala

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[Ayala Allon]

As I understand the answer to my question is yes, but I just want to make sure.

Thanks again

Ayala

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[Tal Galili]

Yes. 

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