Favorite custom functions in R

Return index of entry nearest to a value:

nearest <- function(value, dataset) {
  which(abs(dataset-value)==min(abs(dataset-value)))
}
nearest(pi, 10:1)


Append standard deviation to variable summary:

summary0 <- function(x) {
  print(summary(x));
  cat("Std.Dev.", "\n", sd(x), "\n")
} 
summary0(rnorm(10))


Recode existing variable into percentile scores / percentile ranks:

percentile <- function(x) {
   x <- (x - min(x)) / (max(x) - min(x))
}
x1 <- rnorm(100)
x2 <- percentile(x1)
plot(x1,x2)


See also this post: All things random: Change function defaults in R