Error R Studio Knit HTML with install.packages line

Question

I am a new user to RStudio, and have encountered an error when using a .rmd file and Knit HTML

If I have an install.packages line:

install.packages('ggplot2');
library(ggplot2);

when I click Knit HTML, an error is returned:

Error in contrib.url(repos, "source") : trying to use CRAN without setting a mirror calls: ... withVisible -> eval -> eval -> install.packages -> contrib.url Execution halted

I was able to work around this using:

if (!require('ggplot2')) 
{
  install.packages('ggplot2');
  library(ggplot2);
}

If I'm writing a .rmd, do I need to use the if (!require( line every time I install a new package? Is there a way to avoid this so I can write install.packages( only?

Answer 1

You don't need install.package() line everytime.

Normally you should install packages in console or a separate interactive session or delete that line after installation of that library (here it's ggplot).

Just use library(ggplot2)

  library(ggplot2);

Hope it helps

Answer 2

I was also getting same error while using the Knit document and I did below things in the R script :

1. Run the command in console to set your default repository : options(repos=structure(c(CRAN="http://cran.r-project.org")))

2. Add the below code in your R studio : options(repos="https://cran.rstudio.com" )

3. Add the url reference for packages needed, for example : install.packages("pscl", repos = "https://cran.rstudio.com")