wrap.array

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Reshape an array or a matrix by permuting and/or joining dimensions

Reshape an array or a matrix by permuting and/or joining dimensions. A useful application of this is to reshape a multidimensional array to a matrix, which then can be saved to file using for instance write.table().

Usage
## S3 method for class 'array}(x, map=list(NA), sep=".", ...)':
wrapundefined

 x{An array or a matrix.}
  map{A list of length equal to the number of dimensions in the
    reshaped array.  Each element should be an integer vectors specifying
    the dimensions to be joined in corresponding new dimension.
    One element may equal NA to indicate that that dimension should be
    a join of all non-specified (remaining) dimensions.
    Default is to wrap everything into a vector.
  }
  sep{A character pasting joined dimension names.}
  ...{Not used.}

 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.

 
If the indicies 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.
# 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': ") print(x) cat("\nReshape'x' to its identity: ") 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)): ") 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: ") 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("\nUnwrapmatrix 'y' back to array 'x': ") z <- unwrap(y) print(z) stopifnot(identical(z,x)) cat("\nWrapa matrix 'y' to a vector and back again: ") 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("\nWrapand unwrap a randomly sized and shaped array 'x2': ") maxdim <- 5 dim <- sample(1:maxdim, size=sample(2:maxdim)) 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': ") 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': ") print(map) cat("\nArray'y2': ") y2 <- wrap(x2, map=map) print(y2) cat("\nArray'x2': ") z2 <- unwrap(y2) print(z2) stopifnot(identical(z2,x2)) [object Object] *unwrap(). See aperm(). methods programming
Aliases
  • wrap.array
  • wrap.array
  • wrap.matrix
  • wrap.data.frame
Documentation reproduced from package R.utils, version 0.7.9, License: LGPL version 2.1 or newer (the releases)

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