| fold {future} | R Documentation |
Efficient fold / reduce / accumulate / combine of a vector
fold(x, f, left = TRUE, unname = TRUE, threshold = 1000L)
x |
A vector. |
f |
A binary function, i.e. a function take takes two arguments. |
left |
If 'TRUE', vector is combined from the left (the first element), otherwise the right (the last element). |
unname |
If 'TRUE', function 'f' is called as 'f(unname(y), x[[ii]])', otherwise as 'f(y, x[[ii]])', which may introduce name '"y"'. |
threshold |
An integer (>= 2) specifying the length where the recursive divide'and'conquer call will stop and incremental building of the partial value is performed. Using 'threshold = +Inf' will disable recursive folding. |
In order for recursive folding to give the same results as non-recursive folding, binary function 'f' must be _associative_ with itself, i.e. 'f(f(x[[1]], x[[2]]), x[[3]])' equals 'f(x[[1]], f(x[[2]]), x[[3]])'.
This function is a more efficient (memory and speed) of ['base::Reduce(f, x, right = !left, accumulate = FALSE)'][base::Reduce], especially when 'x' is long.
A vector.