Higher Order Functions in R

higher-order-functions.r

# Dummy attributes matrix
x <- matrix(c(1:12), ncol=4)

# Select attributes for combination (TRUE: in)
s1 <- c(TRUE, TRUE, FALSE, FALSE)
s2 <- c(FALSE, TRUE, FALSE, TRUE)
sel.x <- data.frame(s1, s2)

# Use higher order functions

# Use Map to calculate mean of attributes selected in s1 and s2 (returns list of vectors)
Map(function(p) {rowMeans(x[, p])}, sel.x)

# Reduce returned list using sum '+' (returns vector)
Reduce('+', (Map(function(p) {rowMeans(x[, p])}, sel.x)))

# Reduce previous list using funcion data.frame (returns data.frame!)
Reduce(data.frame, Map(function(p) {rowMeans(x[, p])}, sel.x))