Shuffle Chunks of a Data Frame in R - r

Question

I have a data frame of 90 rows and 90 columns.
My goal is to divide this data frame into 9 pieces, each with 30 rows and 30 columns. Then, I would like to randomly shuffle these 9 pieces for a new data frame.
I'm not sure how to approach this as I'm fairly new in R.
Any help is appreciated!

Answer 1

Use sample on a list of vectors, then unlist and subset:
If I understand rightly, you're trying to do something a bit like one of those 3*3 sliding picture puzzles, right? Where you split the df into chunks of 30 and then 'shuffle' those chunks. This will do that:
### Create a 90 by 90 data frame
set.seed(2)
df <- as.data.frame(array(runif(90*90), dim = c(90,90)))
### Function to randomise subsetting
rand_dims <- function(){
myDims <- list(1:30, 31:60, 61:90)
unlist(sample(myDims))
}
### Shuffle 'chunks' of df
df[rand_dims(), rand_dims()] -> shuffled
### Checking the leading row/col names
### Shows we've succeeded
colnames(shuffled)[1:5]
#> [1] "V61" "V62" "V63" "V64" "V65"
rownames(shuffled)[1:5]
#> [1] "31" "32" "33" "34" "35"
Created on 2021-01-21 by the reprex package (v0.3.0)

Answer 2

Perhaps you can try the following code using split + sample, which helps shuffle the chunks
set.seed(1)
mat <- matrix(data = rnorm(90 * 90), ncol = 90, nrow = 90)
rrnd <- split(sample(seq(nrow(mat))), gl(3, nrow(mat) / 3))
crnd <- split(sample(seq(ncol(mat))), gl(3, ncol(mat) / 3))
mat.shuffle <- c()
for (i in rrnd) {
for (j in crnd) {
mat.shuffle <- c(mat.shuffle, list(mat[i, j]))
}
}
Note that mat.shuffle is a list of 9 chunks. If you want to transform back to the matrix of size 90x90, you can run the code below afterwards
out <- do.call(
rbind,
lapply(
split(
mat.shuffle,
gl(3, length(mat.shuffle) / 3)
),
function(x) do.call(cbind, x)
)
)
and you will see
> str(out)
num [1:90, 1:90] -0.639 -0.984 -0.108 -0.939 1.743 ...
> str(mat.shuffle)
List of 9
$ : num [1:30, 1:30] -0.639 -0.984 -0.108 -0.939 1.743 ...
$ : num [1:30, 1:30] -0.718 -0.154 -0.29 -0.796 1.7 ...
$ : num [1:30, 1:30] -0.886 0.887 -0.381 0.371 0.327 ...
$ : num [1:30, 1:30] -0.4555 -0.901 0.0312 -3.0223 0.8688 ...
$ : num [1:30, 1:30] 0.705 1.559 -1.278 -0.676 1.933 ...
$ : num [1:30, 1:30] -0.1916 -0.98649 -1.65769 0.00104 -0.19544 ...
$ : num [1:30, 1:30] 1.668 -0.869 1.469 -0.222 -1.869 ...
$ : num [1:30, 1:30] 0.9931 0.4116 1.995 -0.4456 -0.0692 ...
$ : num [1:30, 1:30] -1.462 -0.206 1.197 -1.611 -1.708 ...