Reverses some dimensions; a generalization of rev

A multidimensional generalization of rev(): given an array a, and a Boolean vector swap, return an array of the same shape as a but with dimensions corresponding to TRUE elements of swap reversed. If swap is not Boolean, it is interpreted as the dimensions along which to swap.

Usage

arev(a, swap = TRUE)

Arguments

a

Array to be reversed

swap

Vector of Boolean variables. If swap[i] is TRUE, then dimension i of array a is reversed. If swap is of length one, recycle to length(dim(a))

Details

If swap is not Boolean, it is equivalent to 1:n %in% swap (where n is the number of dimensions). Thus multiple entries are ignored, as are entries greater than n.

If a is a vector, rev(a) is returned.

Function arev() handles zero-extent dimensions as expected.

Function arev() does not treat singleton dimensions specially, and is thus different from Octave's flipdim(), which (if supplied with no second argument) flips the first nonsingleton dimension. To reproduce this, use arev(a,fnsd(a)).

Author

Robin K. S. Hankin

See also

ashift

Examples

a <- matrix(1:42,6,7)
arev(a)  #Note swap defaults to TRUE
#>      [,1] [,2] [,3] [,4] [,5] [,6] [,7]
#> [1,]   42   36   30   24   18   12    6
#> [2,]   41   35   29   23   17   11    5
#> [3,]   40   34   28   22   16   10    4
#> [4,]   39   33   27   21   15    9    3
#> [5,]   38   32   26   20   14    8    2
#> [6,]   37   31   25   19   13    7    1

b <- magichypercube.4n(1,d=4)
arev(b,c(TRUE,FALSE,TRUE,FALSE))
#> , , 1, 1
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]   52  201  197   64
#> [2,]  206   55   59  194
#> [3,]  207   54   58  195
#> [4,]   49  204  200   61
#> 
#> , , 2, 1
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]  221   40   44  209
#> [2,]   35  218  214   47
#> [3,]   34  219  215   46
#> [4,]  224   37   41  212
#> 
#> , , 3, 1
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]  237   24   28  225
#> [2,]   19  234  230   31
#> [3,]   18  235  231   30
#> [4,]  240   21   25  228
#> 
#> , , 4, 1
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]    4  249  245   16
#> [2,]  254    7   11  242
#> [3,]  255    6   10  243
#> [4,]    1  252  248   13
#> 
#> , , 1, 2
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]  141  120  124  129
#> [2,]  115  138  134  127
#> [3,]  114  139  135  126
#> [4,]  144  117  121  132
#> 
#> , , 2, 2
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]  100  153  149  112
#> [2,]  158  103  107  146
#> [3,]  159  102  106  147
#> [4,]   97  156  152  109
#> 
#> , , 3, 2
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]   84  169  165   96
#> [2,]  174   87   91  162
#> [3,]  175   86   90  163
#> [4,]   81  172  168   93
#> 
#> , , 4, 2
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]  189   72   76  177
#> [2,]   67  186  182   79
#> [3,]   66  187  183   78
#> [4,]  192   69   73  180
#> 
#> , , 1, 3
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]   77  184  188   65
#> [2,]  179   74   70  191
#> [3,]  178   75   71  190
#> [4,]   80  181  185   68
#> 
#> , , 2, 3
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]  164   89   85  176
#> [2,]   94  167  171   82
#> [3,]   95  166  170   83
#> [4,]  161   92   88  173
#> 
#> , , 3, 3
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]  148  105  101  160
#> [2,]  110  151  155   98
#> [3,]  111  150  154   99
#> [4,]  145  108  104  157
#> 
#> , , 4, 3
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]  125  136  140  113
#> [2,]  131  122  118  143
#> [3,]  130  123  119  142
#> [4,]  128  133  137  116
#> 
#> , , 1, 4
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]  244    9    5  256
#> [2,]   14  247  251    2
#> [3,]   15  246  250    3
#> [4,]  241   12    8  253
#> 
#> , , 2, 4
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]   29  232  236   17
#> [2,]  227   26   22  239
#> [3,]  226   27   23  238
#> [4,]   32  229  233   20
#> 
#> , , 3, 4
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]   45  216  220   33
#> [2,]  211   42   38  223
#> [3,]  210   43   39  222
#> [4,]   48  213  217   36
#> 
#> , , 4, 4
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]  196   57   53  208
#> [2,]   62  199  203   50
#> [3,]   63  198  202   51
#> [4,]  193   60   56  205
#>