Reshape an array or a matrix by permuting and/or joining dimensions
Reshape an array or a matrix by permuting and/or joining dimensions.
## S3 method for class 'array' wrap(x, map=list(NA), sep=".", ...)
x |
|
map |
A |
sep |
A |
... |
Not used. |
If the indices in unlist(map) is in a non-increasing order,
aperm() will be called, which requires reshuffling
of array elements in memory. In all other cases, the reshaping of the
array does not require this, but only fast modifications of
attributes dim and dimnames.
Returns an array of length(map) dimensions, where the first
dimension is of size prod(map[[1]]), the second
prod(map[[2]]), and so on.
Henrik Bengtsson
# Create a 3x2x3 array
dim <- c(3,2,3)
ndim <- length(dim)
dimnames <- list()
for (kk in 1:ndim)
dimnames[[kk]] <- sprintf("%s%d", letters[kk], 1:dim[kk])
x <- 1:prod(dim)
x <- array(x, dim=dim, dimnames=dimnames)
cat("Array 'x':\n")
print(x)
cat("\nReshape 'x' to its identity:\n")
y <- wrap(x, map=list(1, 2, 3))
print(y)
# Assert correctness of reshaping
stopifnot(identical(y, x))
cat("\nReshape 'x' by swapping dimensions 2 and 3, i.e. aperm(x, perm=c(1,3,2)):\n")
y <- wrap(x, map=list(1, 3, 2))
print(y)
# Assert correctness of reshaping
stopifnot(identical(y, aperm(x, perm=c(1,3,2))))
cat("\nWrap 'x' to a matrix 'y' by keeping dimension 1 and joining the others:\n")
y <- wrap(x, map=list(1, NA))
print(y)
# Assert correctness of reshaping
for (aa in dimnames(x)[[1]]) {
for (bb in dimnames(x)[[2]]) {
for (cc in dimnames(x)[[3]]) {
tt <- paste(bb, cc, sep=".")
stopifnot(identical(y[aa,tt], x[aa,bb,cc]))
}
}
}
cat("\nUnwrap matrix 'y' back to array 'x':\n")
z <- unwrap(y)
print(z)
stopifnot(identical(z,x))
cat("\nWrap a matrix 'y' to a vector and back again:\n")
x <- matrix(1:8, nrow=2, dimnames=list(letters[1:2], 1:4))
y <- wrap(x)
z <- unwrap(y)
print(z)
stopifnot(identical(z,x))
cat("\nWrap and unwrap a randomly sized and shaped array 'x2':\n")
maxdim <- 5
dim <- sample(1:maxdim, size=sample(2:maxdim, size=1))
ndim <- length(dim)
dimnames <- list()
for (kk in 1:ndim)
dimnames[[kk]] <- sprintf("%s%d", letters[kk], 1:dim[kk])
x2 <- 1:prod(dim)
x2 <- array(x, dim=dim, dimnames=dimnames)
cat("\nArray 'x2':\n")
print(x)
# Number of dimensions of wrapped array
ndim2 <- sample(1:(ndim-1), size=1)
# Create a random map for joining dimensions
splits <- NULL
if (ndim > 2)
splits <- sort(sample(2:(ndim-1), size=ndim2-1))
splits <- c(0, splits, ndim)
map <- list()
for (kk in 1:ndim2)
map[[kk]] <- (splits[kk]+1):splits[kk+1]
cat("\nRandom 'map':\n")
print(map)
cat("\nArray 'y2':\n")
y2 <- wrap(x2, map=map)
print(y2)
cat("\nArray 'x2':\n")
z2 <- unwrap(y2)
print(z2)
stopifnot(identical(z2,x2))Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.