Subsetting a SparseArray object

Like ordinary arrays in base R, SparseArray derivatives support subsetting via the single bracket operator ([).
Examples

a <- array(0L, dim=5:3)
a[c(1:2, 8, 10, 15:17, 20, 24, 40, 56:60)] <- (1:15)*10L
svt <- SparseArray(a)
svt
#> <5 x 4 x 3 SparseArray> of type "integer" [nzcount=15 (25%)]:
#> ,,1
#>      [,1] [,2] [,3] [,4]
#> [1,]   10    0    0   60
#> [2,]   20    0    0   70
#> [3,]    0   30    0    0
#> [4,]    0    0    0    0
#> [5,]    0   40   50   80
#> 
#> ,,2
#>      [,1] [,2] [,3] [,4]
#> [1,]    0    0    0    0
#> [2,]    0    0    0    0
#> [3,]    0    0    0    0
#> [4,]   90    0    0    0
#> [5,]    0    0    0  100
#> 
#> ,,3
#>      [,1] [,2] [,3] [,4]
#> [1,]    0    0    0  110
#> [2,]    0    0    0  120
#> [3,]    0    0    0  130
#> [4,]    0    0    0  140
#> [5,]    0    0    0  150
#> 

## ---------------------------------------------------------------------
## N-dimensional subsetting
## ---------------------------------------------------------------------
svt[5:3, c(4,2,4), 2:3]
#> <3 x 3 x 2 SparseArray> of type "integer" [nzcount=8 (44%)]:
#> ,,1
#>      [,1] [,2] [,3]
#> [1,]  100    0  100
#> [2,]    0    0    0
#> [3,]    0    0    0
#> 
#> ,,2
#>      [,1] [,2] [,3]
#> [1,]  150    0  150
#> [2,]  140    0  140
#> [3,]  130    0  130
#> 
svt[ , c(4,2,4), 2:3]
#> <5 x 3 x 2 SparseArray> of type "integer" [nzcount=12 (40%)]:
#> ,,1
#>      [,1] [,2] [,3]
#> [1,]    0    0    0
#> [2,]    0    0    0
#> [3,]    0    0    0
#> [4,]    0    0    0
#> [5,]  100    0  100
#> 
#> ,,2
#>      [,1] [,2] [,3]
#> [1,]  110    0  110
#> [2,]  120    0  120
#> [3,]  130    0  130
#> [4,]  140    0  140
#> [5,]  150    0  150
#> 
svt[ , c(4,2,4), -1]
#> <5 x 3 x 2 SparseArray> of type "integer" [nzcount=12 (40%)]:
#> ,,1
#>      [,1] [,2] [,3]
#> [1,]    0    0    0
#> [2,]    0    0    0
#> [3,]    0    0    0
#> [4,]    0    0    0
#> [5,]  100    0  100
#> 
#> ,,2
#>      [,1] [,2] [,3]
#> [1,]  110    0  110
#> [2,]  120    0  120
#> [3,]  130    0  130
#> [4,]  140    0  140
#> [5,]  150    0  150
#> 
svt[ , c(4,2,4), 1]
#> <5 x 3 SparseMatrix> of type "integer" [nzcount=8 (53%)]:
#>      [,1] [,2] [,3]
#> [1,]   60    0   60
#> [2,]   70    0   70
#> [3,]    0   30    0
#> [4,]    0    0    0
#> [5,]   80   40   80

svt2 <- svt[ , c(4,2,4), 1, drop=FALSE]
svt2
#> <5 x 3 x 1 SparseArray> of type "integer" [nzcount=8 (53%)]:
#> ,,1
#>      [,1] [,2] [,3]
#> [1,]   60    0   60
#> [2,]   70    0   70
#> [3,]    0   30    0
#> [4,]    0    0    0
#> [5,]   80   40   80
#> 

## Ineffective dimensions can always be dropped as a separate step:
drop(svt2)
#> <5 x 3 SparseMatrix> of type "integer" [nzcount=8 (53%)]:
#>      [,1] [,2] [,3]
#> [1,]   60    0   60
#> [2,]   70    0   70
#> [3,]    0   30    0
#> [4,]    0    0    0
#> [5,]   80   40   80

svt[ , c(4,2,4), integer(0)]
#> <5 x 3 x 0 SparseArray> of type "integer" [nzcount=0 (NaN%)]

dimnames(a) <- list(letters[1:5], NULL, LETTERS[1:3])
svt <- SparseArray(a)

svt[c("d", "a"), c(4,2,4), "C"]
#> <2 x 3 SparseMatrix> of type "integer" [nzcount=4 (67%)]:
#>   [,1] [,2] [,3]
#> d  140    0  140
#> a  110    0  110

svt2 <- svt["e", c(4,2,4), , drop=FALSE]
svt2
#> <1 x 3 x 3 SparseArray> of type "integer" [nzcount=7 (78%)]:
#> ,,A
#>   [,1] [,2] [,3]
#> e   80   40   80
#> 
#> ,,B
#>   [,1] [,2] [,3]
#> e  100    0  100
#> 
#> ,,C
#>   [,1] [,2] [,3]
#> e  150    0  150
#> 

drop(svt2)
#> <3 x 3 SparseMatrix> of type "integer" [nzcount=7 (78%)]:
#>        A   B   C
#> [1,]  80 100 150
#> [2,]  40   0   0
#> [3,]  80 100 150

## ---------------------------------------------------------------------
## 1D-style subsetting (a.k.a. linear subsetting)
## ---------------------------------------------------------------------

## Using a numeric vector (L-index):
svt[c(60, 24, 21, 56)]
#> [1] 150  90   0 110

## Using a matrix subscript (M-index):
m <- rbind(c(5, 4, 3),
           c(4, 1, 2),
           c(1, 1, 2),
           c(1, 4, 3))
svt[m]
#> [1] 150  90   0 110

## See '?Lindex2Mindex' in the S4Arrays package for how to convert an
## L-index to an M-index and vice-versa.

## ---------------------------------------------------------------------
## Sanity checks
## ---------------------------------------------------------------------
svt2 <- svt[5:3, c(4,2,4), 2:3]
a2   <- a  [5:3, c(4,2,4), 2:3]
stopifnot(identical(as.array(svt2), a2), identical(svt2, SparseArray(a2)))
svt2 <- svt[ , c(4,2,4), 2:3]
a2   <- a  [ , c(4,2,4), 2:3]
stopifnot(identical(as.array(svt2), a2), identical(svt2, SparseArray(a2)))
svt2 <- svt[ , c(4,2,4), -1]
a2   <- a  [ , c(4,2,4), -1]
stopifnot(identical(as.array(svt2), a2), identical(svt2, SparseArray(a2)))
svt2 <- svt[ , c(4,2,4), 1]
a2   <- a  [ , c(4,2,4), 1]
stopifnot(identical(as.array(svt2), a2), identical(svt2, SparseArray(a2)))
svt2 <- svt[ , c(4,2,4), 1, drop=FALSE]
a2   <- a  [ , c(4,2,4), 1, drop=FALSE]
stopifnot(identical(as.array(svt2), a2), identical(svt2, SparseArray(a2)))
svt2 <- drop(svt2)
a2 <- drop(a2)
stopifnot(identical(as.array(svt2), a2), identical(svt2, SparseArray(a2)))
svt2 <- svt[ , c(4,2,4), integer(0)]
a2   <- a  [ , c(4,2,4), integer(0)]
stopifnot(identical(as.array(svt2), a2),
          identical(unname(svt2), unname(SparseArray(a2))))
svt2 <- svt[c("d", "a"), c(4,2,4), "C"]
a2   <- a  [c("d", "a"), c(4,2,4), "C"]
stopifnot(identical(as.array(svt2), a2), identical(svt2, SparseArray(a2)))
svt2 <- svt["e", c(4,2,4), , drop=FALSE]
a2   <- a  ["e", c(4,2,4), , drop=FALSE]
stopifnot(identical(as.array(svt2), a2), identical(svt2, SparseArray(a2)))
svt2 <- drop(svt2)
a2 <- drop(a2)
stopifnot(identical(as.array(svt2), a2), identical(svt2, SparseArray(a2)))
stopifnot(identical(svt[c(60, 24, 21, 56)], svt[m]))
See also

Examples
