R Under development (unstable) (2024-09-10 r87115 ucrt) -- "Unsuffered Consequences"
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> library(abind)
> options(error=function() NULL)
> x <- array(0, dim=c(2,3,4),dimnames=list(letters[1:2],LETTERS[1:3],letters[23:26]))
> # What we want to do here is get slices x[i,c("A","B"),c("w","x","y")] (for all i)
> # to be matrix(1:6,ncol=3).
> # If we assign in the standard way, and specify submatrices of the same shape in
> # indices and as the value of the assign (but leave some indices on the LHS empty),
> # then it is possible that submatrices do not end up being assigned to in the way
> # we might expect, because the RHS value is flattened and replicated.
> # This is only a problem when the repeating index has a lower dim number (here 1)
> # than the specified indices (here 2 and 3).
> x[,c("A","B"),c("w","x","y")] <- matrix(1:6,ncol=3)
> x[1,c("A","B"),c("w","x","y")]
  w x y
A 1 5 3
B 3 1 5
> x[2,c("A","B"),c("w","x","y")]
  w x y
A 2 6 4
B 4 2 6
> # Assign in a way so that the RHS has its elements laid out in the same way
> # as the LHS.
> x[,c("A","B"),c("w","x","y")] <- rep(matrix(1:6,ncol=3), each=2)
> # first slice
> x[1,c("A","B"),c("w","x","y")]
  w x y
A 1 3 5
B 2 4 6
> # second slice
> x[2,c("A","B"),c("w","x","y")]
  w x y
A 1 3 5
B 2 4 6
> 
> # now do it with afill()
> x[] <- 0
> afill(x, TRUE, , ) <- matrix(1:6,ncol=3, dimnames=list(c("A","B"),c("w","x","y")))
> x[1,c("A","B"),c("w","x","y")]
  w x y
A 1 3 5
B 2 4 6
> x[2,c("A","B"),c("w","x","y")]
  w x y
A 1 3 5
B 2 4 6
> # mix up the order of the RHS of the assignment, afill will sort it back to match the LHS
> x[] <- 0
> afill(x, T, , ) <- matrix(1:6,ncol=3, dimnames=list(c("A","B"),c("w","x","y")))[2:1,]
> x[1,c("A","B"),c("w","x","y")]
  w x y
A 1 3 5
B 2 4 6
> x[2,c("A","B"),c("w","x","y")]
  w x y
A 1 3 5
B 2 4 6
> table(x==0)

FALSE  TRUE 
   12    12 
> 
> # 4-d example
> x <- array(0, dim=c(2,3,3,4),dimnames=list(letters[1:2],LETTERS[1:3],letters[24:26],LETTERS[23:26]))
> x[1,c("A","B"),1,c("W","X","Y")] <- 1:6
> x[1,c("A","B"),2,c("W","X","Y")] <- 1:6
> x[1,c("A","B"),3,c("W","X","Y")] <- 1:6
> x[2,c("A","B"),1,c("W","X","Y")] <- 1:6
> x[2,c("A","B"),2,c("W","X","Y")] <- 1:6
> x[2,c("A","B"),3,c("W","X","Y")] <- 1:6
> c(x[1:2,c("A","B"),1:3,c("W","X","Y")])
 [1] 1 1 2 2 1 1 2 2 1 1 2 2 3 3 4 4 3 3 4 4 3 3 4 4 5 5 6 6 5 5 6 6 5 5 6 6
> c(matrix(1:6, ncol=3)[rep(1:2, each=2),rep(1:3,each=3)])
 [1] 1 1 2 2 1 1 2 2 1 1 2 2 3 3 4 4 3 3 4 4 3 3 4 4 5 5 6 6 5 5 6 6 5 5 6 6
> 
> afill(x, T, , T, ) <- matrix(1:6,ncol=3, dimnames=list(c("A","B"),c("W","X","Y")))
> x[1,c("A","B"),1,c("W","X","Y")]
  W X Y
A 1 3 5
B 2 4 6
> x[1,c("A","B"),2,c("W","X","Y")]
  W X Y
A 1 3 5
B 2 4 6
> x[1,c("A","B"),3,c("W","X","Y")]
  W X Y
A 1 3 5
B 2 4 6
> x[2,c("A","B"),1,c("W","X","Y")]
  W X Y
A 1 3 5
B 2 4 6
> x[2,c("A","B"),2,c("W","X","Y")]
  W X Y
A 1 3 5
B 2 4 6
> x[2,c("A","B"),3,c("W","X","Y")]
  W X Y
A 1 3 5
B 2 4 6
> table(x==0)

FALSE  TRUE 
   36    36 
> 
> # 2-d example
> x <- array(1:24, dim=c(6,4), dimnames=list(LETTERS[1:6], letters[23:26]))
> x1 <- x
> x1[2:4,2:3] <- -(1:6)
> x1
  w  x  y  z
A 1  7 13 19
B 2 -1 -4 20
C 3 -2 -5 21
D 4 -3 -6 22
E 5 11 17 23
F 6 12 18 24
> x1 <- x
> x1[LETTERS[2:4],letters[24:25]] <- -(1:6)
> x1
  w  x  y  z
A 1  7 13 19
B 2 -1 -4 20
C 3 -2 -5 21
D 4 -3 -6 22
E 5 11 17 23
F 6 12 18 24
> x2 <- x
> afill(x2) <- array(-(1:6),dim=c(3,2), dimnames=list(LETTERS[2:4],letters[24:25]))
> x2
  w  x  y  z
A 1  7 13 19
B 2 -1 -4 20
C 3 -2 -5 21
D 4 -3 -6 22
E 5 11 17 23
F 6 12 18 24
> identical(x1, x2)
[1] TRUE
> x2 <- x
> afill(x2) <- array(-(1:6),dim=c(3,2), dimnames=list(LETTERS[5:7],letters[24:25]))
Error in `afill<-.default`(`*tmp*`, value = -1:-6) : 
  value has dimnames that are not in 'x' on dim[1]: 'G'
Calls: afill<- -> afill<-.default
> x2 <- x
> afill(x2,excess.ok=T) <- array(-(1:6),dim=c(3,2), dimnames=list(LETTERS[5:7],letters[24:25]))
> x2
  w  x  y  z
A 1  7 13 19
B 2  8 14 20
C 3  9 15 21
D 4 10 16 22
E 5 -1 -4 23
F 6 -2 -5 24
> x2 <- x
> afill(x2, local=T) <- array(-(1:6),dim=c(3,2), dimnames=list(LETTERS[2:4],letters[24:25]))
> x2
  w  x  y  z
A 1  7 13 19
B 2 -1 -4 20
C 3 -2 -5 21
D 4 -3 -6 22
E 5 11 17 23
F 6 12 18 24
> 
> # 1-d named-vector example
> x <- c(A=0,B=0,C=0,D=0)
> afill(x) <- c(B=1,C=2)
> x
A B C D 
0 1 2 0 
> # return value is the part of x that is assigned to
> (afill(x) <- c(B=1,C=2))
B C 
1 2 
> (x[2:3] <- 0)
[1] 0
> 
> proc.time()
   user  system elapsed 
   0.12    0.06    0.17