Subset an Array

Extracts a subset from an array. You can also use the [ operator. Supports R-style indexing including scalar indices (which drop axes), ranges (a:b), array(c(...)) for selecting multiple elements along an axis, and boolean masks.

Usage

# S3 method for class 'AnvlArray'
x[...]

nv_subset(x, ...)

Arguments

x

(arrayish)
One input. Can be any data type. An R value materializes at its default data type.

...

Subset specifications, one per axis. Omitted trailing axes select all elements.

A boolean mask (an R logical array such as arr(TRUE, FALSE), or an arrayish value of dtype bool) selects the elements at the TRUE positions. A mask for one axis must have as many elements as the size of that axis. A mask that is the only subscript and has the same shape as x selects across the whole array, yielding a 1-D result. Under jit(), the values of a mask must be known at compile time, because the number of selected elements determines the output shape: R logical arrays and arrays created in or closed over by the function work, a mask computed from the function's inputs does not.

See the Subsetting article for details.

Value

(arrayish)
Has the input's data type, and the shape the specifications select – a scalar index drops its axis, a range, an index array or an axis mask keeps it, and a whole-array mask yields a 1-D result.

See also

nv_subset_assign() for updating subsets, the Subsetting article for a comprehensive guide.

Examples

x <- nv_matrix(1:12, nrow = 3)
x
#> AnvlArray
#>   1  4  7 10
#>   2  5  8 11
#>   3  6  9 12
#> [ CPUi32{3,4} ] 
# select row 2
nv_subset(x, 2)
#> AnvlArray
#>   2
#>   5
#>   8
#>  11
#> [ CPUi32{4} ] 
x[2, ]
#> AnvlArray
#>   2
#>   5
#>   8
#>  11
#> [ CPUi32{4} ] 

# select rows 1 to 2, all columns
nv_subset(x, 1:2)
#> AnvlArray
#>   1  4  7 10
#>   2  5  8 11
#> [ CPUi32{2,4} ] 
x[1:2, ]
#> AnvlArray
#>   1  4  7 10
#>   2  5  8 11
#> [ CPUi32{2,4} ] 

# Select rows 1 and 3 with a mask
x[arr(TRUE, FALSE, TRUE), ]
#> AnvlArray
#>   1  4  7 10
#>   3  6  9 12
#> [ CPUi32{2,4} ] 

# Select all elements greater than 6 (not in `jit()`, see above)
x[x > 6]
#> AnvlArray
#>   7
#>   8
#>   9
#>  10
#>  11
#>  12
#> [ CPUi32{6} ]