with() function applies an expression to a dataset.
#with(data,expression)
By() function applies a function t each level of a factors.
#by(data,factorlist,function)
Consider a related program for the above differentiation.
if(!require(package, character.only=T, quietly=T)) {
install.packages (package)
library(package, character.only=T)
}
For multiple packages you can use
for(package in c(’’, ‘’)) {
if(!require(package, character.only=T, quietly=T)) {
install.packages (package)
library(package, character.only=T)
}
}