Serpentine design and sorting
September 19, 2020
Take a grid and serpentine it row-wise or column-wise
This fn joins two matrices alternately columnwise, which is why this is the source of inspiration for generating serpentine design.
alternate.cols <- function(m1, m2) {
cbind(m1, m2)[, order(c(seq(ncol(m1)), seq(ncol(m2))))]
}
A custom function to create a serpentine design in whatever fashion specified:
serpentine <- function(x, columnwise=TRUE){
if (columnwise) {
odd <- x[, seq(1, by=2, length.out = ncol(x)/2)] # odd x
rev_even <- x[, seq(from = 2,
by=2,
length.out = (ifelse((ncol(x)%%2 != 0),
((ncol(x)/2)-1),
(ncol(x)/2))))][seq(dim(x)[1],1),] # or, even[rev(1:nrow(x)),] # reversed even x
alternate_cbind <- cbind(odd, rev_even)[, order(c(seq(ncol(odd)),
seq(ncol(rev_even))))]
return(alternate_cbind)}
else {
odd <- x[seq(1, by=2, length.out = nrow(x)/2),] # odd x
rev_even <- x[seq(from = 2, by=2, length.out = (ifelse((nrow(x)%%2 != 0),
((nrow(x)/2)-1),
(nrow(x)/2)))), ][, seq(dim(x)[2],1)] # or, even[, rev(1:ncol(x))] # reversed even x
alternate_rbind <- rbind(odd, rev_even)[order(c(seq(nrow(odd)),
seq(nrow(rev_even)))), ]
return(alternate_rbind)
}
}
Let’s see the function in action
grid <- matrix(seq(from = 1, by = 1, length.out = 6*7), nrow = 6, byrow = TRUE)
serpentine(grid, columnwise = TRUE)
## [,1] [,2] [,3] [,4] [,5] [,6] [,7]
## [1,] 1 37 3 39 5 41 7
## [2,] 8 30 10 32 12 34 14
## [3,] 15 23 17 25 19 27 21
## [4,] 22 16 24 18 26 20 28
## [5,] 29 9 31 11 33 13 35
## [6,] 36 2 38 4 40 6 42
serpentine(grid, columnwise = FALSE)
## [,1] [,2] [,3] [,4] [,5] [,6] [,7]
## [1,] 1 2 3 4 5 6 7
## [2,] 14 13 12 11 10 9 8
## [3,] 15 16 17 18 19 20 21
## [4,] 28 27 26 25 24 23 22
## [5,] 29 30 31 32 33 34 35
## [6,] 42 41 40 39 38 37 36
Test it with any design matrix, such as one below:
design_mat <- data.frame(row = c(rep(letters[1:4], each = 5)), col = c(rep(letters[22:26], times = 4)))
serpentine_sorter() requires serpentine() to be available in the namespace to work.
Given a row-col ordering of a design, this function will convert any vector of that order to serpentine sorted order.
serpentine_sorter <- function(x, ncols, byrow = FALSE, columnwise = FALSE){
# Arguments
# x vector which will be re-ordered
# ncols An integer specifying number of columns in design matrix where x belongs to
# byrow Logical: is the design matrix order filled column-level wise(_first_) and row-level wise(_second_)?
# Note that here, the name of argument is somewhat misleading. Look [sorting](./sorting.R) example
# to learn how sorting is done with multiple column specifications.
# columnwise Logical: Should the serpentine generation be done column wise or row wise?
as.vector(t(serpentine(matrix(rev(x), ncol = ncols,
byrow = byrow)[, ncols:1],
columnwise = columnwise)))
}
Test with a vector x in a row-col design matrix with 20 columns ordered column-level wise(first) followed by row-level wise(second).
## or the following will generate necessary length of index
row_a <- 1:20
col_b <- 1:12
addition <- rep(seq(0, by = length(row_a), length.out = length(col_b)), each = length(row_a))
revved <- rep(c(row_a, rev(row_a)), times = length(col_b)/2)
alternating <- addition + revved
length(alternating)
## [1] 240
- Posted on:
- September 19, 2020
- Length:
- 3 minute read, 514 words