install.R

#---------------------------------------------------------------
# INSTALL MY PACKAGES SNIPPET install.R
#---------------------------------------------------------------

# Script to detach all previous packages loaded, install those who you
# use and import them. Change the needed argument to install others or paste to your script
# the install_my_packages() fucntion and give other argument

#
# USEFUL:
# use this code to your source script to 
# rm(list=ls())
# setwd("~/home/project/")
# source("./utils/install.R")
# install_and_detach()


install_and_detach <- function(needed = c(
                            "Rmisc", 
                            "dplyr",
                            "doBy",
                            "lme4",
                            "gmodels",
                            "lattice",
                            "ggplot2"),
                          clean = TRUE,
                          load = FALSE )
{
    
  # @needed is a vector of package to install. Set the default option as your basics
  # @clean logical. If TRUE, all all packages are detached
  # @load logical. If TRUE, all packages will be loaded
  if(clean == TRUE ) {
    # taken from: http://stackoverflow.com/questions/7505547/detach-all-packages-while-working-in-r
    basic.packages <- c("package:stats","package:graphics","package:grDevices",
                      "package:utils","package:datasets","package:methods","package:base")
    package.list <- search()[ifelse(unlist(gregexpr("package:",search()))==1,TRUE,FALSE)]
    package.list <- setdiff(package.list,basic.packages)
    if (length(package.list)>0)  for (package in package.list) detach(package, character.only=TRUE)
  }




  
   unlist(lapply(needed, FUN = function(x){
    if(!x %in% installed.packages()){
      cat("====================================================\n")
      cat("The following package will be installed ",x, "\n")
      install.packages(x)
      cat("====================================================\n")
    }
    if(load == TRUE)  
      {
      library(x, character.only = T, verbose = F)
      return(paste0( x , " successfully loaded"))
      }
    }))
}

With lapply may be quiet quicker. So, with "for" it is good enough may be the same speed for both unless you install 1000 packages

needed <- list("ggplot2", "data.table", "png", "jpeg", "grid")
unlist(lapply(needed, FUN = function(x){
if(!x %in% installed.packages()){
cat("====================================================\n")
cat("The following package will be installed ",x, "\n")
install.packages(x)
cat("====================================================\n")
}
library(x, character.only = T, verbose = F)
return(paste0( x , " successfully loaded"))
}))

Thanks : ) I will apply your recomendation.

Updated now has more options : )

Your solution for the loading is very clever and readeable