R - How to get a difference/sum of 2 step functions?

Question

I have 2 step function objects (ecdf objects to be exact). How to calculate a step function that is a difference or sum of these two?

Answer 1

I just had the same question and found the follwoing nice solution

y1 <- c(0, 1, 2, 0)
x1 <- c(1, 2, 3)
f1 <- stepfun(x = x1, y = y1)
par(mfrow = c(2, 2))
plot(f1)

y2 <- c(0, 1, 0)
x2 <- c(1.5, 2.5)
f2 <- stepfun(x = x2, y = y2)
plot(f2)

fs <- function(x, f1, f2) {
  return(f1(x) + f2(x))
}

fm <- function(x, f1, f2) {
  return(f1(x) * f2(x))
}

x <- seq(0, 4, length.out = 100)
plot(x, fs(x, f1, f2), type = "s", main = "Sum f1+f2")
plot(x, fm(x, f1, f2), type = "s", main = "Multiplication f1*f2")

par(mfrow = c(1, 1))

There might be a more elegant version using + and * operators, see e.g. here...

foo <- structure(list(value = 1, txt = 'a'), class = 'foo')
`+.foo` <- function(leftfoo, rightfoo) { return (paste(leftfoo$txt, rightfoo$txt)) }

foo + foo
#[1] "a a"