Rにおける高階関数はCommon Higher-Order Functions in Functional Programming Languagesにあるように一通りそろっている
Reduce uses a binary function to successively combine the elements of a given vector and a possibly given initial value. Filter extracts the elements of a vector for which a predicate (logical) function gives true. Find and Position give the first or last such element and its position in the vector, respectively. Map applies a function to the corresponding elements of given vectors. Negate creates the negation of a given function.
foldl,foldrも簡単
foldl <- function(f,x,i){Reduce(f,x,i)}
foldr <- function(f,x,i){Reduce(f,x,i,right=TRUE)}
実行してみる
> foldl("-",list(1,2,3),1) # ((1-1)-2)-3
[1] -5
> foldr("-",list(1,2,3),1) # 1-(2-(3-1))
[1] 1
あとRの高階関数は大文字で始める規則にでもなってんのかな？
Rの基礎とプログラミング技法