R: standard error functions for use in ggplot2

standard_error.R

# standard error function
stderr <- function(x) {
          sqrt(var(x[!is.na(x)]) / length(x[!is.na(x)]))
}

# Then create a wrapper to *stderr* to make it compatible with *stat_summary*
my.stderr <- function(x) {
             meany <- mean(x)
             ymin  <- mean(x) - stderr(x)
             ymax  <- mean(x) + stderr(x)
             # assemble the named output
             out <- c(y = meany, ymin = ymin, ymax = ymax)
             return(out)
}