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Functions are either built-in or user-defined sets of encapsulated commands which may take any number of arguments. Preface a function with the function statement and use the <- operator to assign functions to objects in your workspace.
You may use functions to run the same procedure on different objects in your workspace. For example,
check <- function(p, q) {
result <- (p - q)/q
result
}
is a simple function with arguments p and q which
calculates the difference between the 4#4
th elements of the vector
p and the 4#4
th element of the vector q as a proportion of
the 4#4
th element of q, and returns the resulting vector. For
example, check(p = 10, q = 2) returns 4. You may omit the
descriptors as long as you keep the arguments in the correct order:
check(10, 2) also returns 4. You may also use other objects as
inputs to the function. If again = 10 and really = 2,
then check(p = again, q = really) and check(again, really)
also returns 4.
Because functions run commands as a set, you should make sure that each command in your function works by testing each line of the function at the R prompt.