foldblock: Successively apply a function to adjacent blocks of a...
In lambda.tools: Tools for Modeling Data with Functional Programming

Description Arguments Value Usage Details Author(s) See Also Examples

Apply a function to non-overlapping sub-sequences and the accumulated value of the function application

`x`	Any indexable data structure
`window`	The number of elements in each sub-sequence
`fn`	The function applied to the sub-sequence
`acc`	The intermediate accumulated value

The accumulated value

foldblock(x, window, fn, acc=0)

This function is the fold counterpart of mapblock. Like mapblock the usefulness of this function is for the 2D case, as it can simplify interacting with matrices. See the example below for using foldblock as a summation operator over matrices

Brian Lee Yung Rowe

map fold foldrange

# Sum 5 2 x 2 matrices
ms <- matrix(sample(40,20, replace=TRUE), nrow=2)
foldblock(ms,2, function(a,b) a + b)

# 1D foldblock is equivalent to 2D fold
x <- 1:12
f <- function(a,b) mean(a) + b
foldblock(x,3,f) == fold(matrix(x, nrow=3),f, 0)