Check for installed packages before running install.packages() [duplicate]

Question

try: require("xtable") or "xtable" %in% rownames(installed.packages())

If you want to do it as simply as possible:

packages <- c("ggplot2", "dplyr", "Hmisc", "lme4", "arm", "lattice", "lavaan")

install.packages(setdiff(packages, rownames(installed.packages())))  

Replace the packages listed on the first line by those needed to run your code, and voilà!

Note: Edited to remove conditional wrapper thanks to Artem's comment below.

This is a function I often used to check for a package, install it otherwise and load again:

pkgTest <- function(x)
  {
    if (!require(x,character.only = TRUE))
    {
      install.packages(x,dep=TRUE)
        if(!require(x,character.only = TRUE)) stop("Package not found")
    }
  }

Works like pkgTest("xtable"). It only works if the mirror is set though, but you could enter that in the require calls.

I suggest a more lightweight solution using system.file.

is_inst <- function(pkg) {
    nzchar(system.file(package = pkg))
}

is_inst2 <- function(pkg) {
    pkg %in% rownames(installed.packages())
}

library(microbenchmark)
microbenchmark(is_inst("aaa"), is_inst2("aaa"))
## Unit: microseconds
##            expr      min        lq       mean    median       uq       max neval
##  is_inst("aaa")   22.284   24.6335   42.84806   34.6815   47.566   252.568   100
## is_inst2("aaa") 1099.334 1220.5510 1778.57019 1401.5095 1829.973 17653.148   100
microbenchmark(is_inst("ggplot2"), is_inst2("ggplot2"))
## Unit: microseconds
##                expr      min       lq     mean   median       uq      max neval
##  is_inst("ggplot2")  336.845  386.660  459.243  431.710  483.474  867.637   100
## is_inst2("ggplot2") 1144.613 1276.847 1507.355 1410.054 1656.557 2747.508   100