Select Elements Along an Axis

Picks one or more elements along axis axis of x. Use this instead of [ or nv_subset when the index to select is provided programmatically.

Usage

nv_select(x, axis, index)

Arguments

x

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

axis

(integer(1))
Axis to index into. Negative values count from the end, i.e. -1 refers to the last axis.

index

(arrayish)
Scalar or 1-D array of an integer data type, which it keeps – the index takes no part in x's data type.

Value

(arrayish)
Has x's data type. axis is dropped if index was scalar, and otherwise resized to the number of selected elements.

See also

nv_subset() for general subsetting, prim_static_slice().

Examples

# a scalar index drops the axis, an index array keeps it
m <- nv_matrix(1:6, nrow = 2)
nv_select(m, axis = 2L, index = 2L)
#> AnvlArray
#>  3
#>  4
#> [ CPUi32{2} ] 
nv_select(m, axis = 1L, index = 1L)
#> AnvlArray
#>  1
#>  3
#>  5
#> [ CPUi32{3} ] 
nv_select(m, axis = 2L, index = array(c(1L, 3L)))
#> AnvlArray
#>  1 5
#>  2 6
#> [ CPUi32{2,2} ]