Coordinate-based indexing

sel() selects data by coordinate value (label-based). isel() selects data by integer index (position-based).

Usage

isel(.data, ...)

sel(.data, ...)

Arguments

.data

A Variable, DataArray, or Dataset

...

Named arguments specifying the selection. For sel(), values are coordinate values. For isel(), values are integer indices (1-based). Use a vector for ranges: sel(da, lat = c(-30, 30)) selects the range. Use a scalar for a single position: isel(da, time = 1) picks one index and drops that dimension.

Value

Same type as input, with dimensions sliced or dropped.

Details

Both work on Variables, DataArrays, and Datasets, and return objects of the same type with dimensions correctly updated.

Examples

v <- Variable(
  dims = c("lat", "lon"),
  data = matrix(1:12, 3, 4)
)
da <- DataArray(
  variable = v,
  coords = list(
    lat = ImplicitCoord(dimension = "lat", n = 3L, offset = -10, step = 10),
    lon = ImplicitCoord(dimension = "lon", n = 4L, offset = 100, step = 10)
  )
)

# Select by coordinate value
sel(da, lat = 0)             # single latitude, drops lat dim
#> <DataArray> '(unnamed)'
#>   Dimensions:  (lon: 4)
#>   Coordinates:
#>     * lon  (lon) 100 to 130
#>   dtype: integer  (16 B)
sel(da, lat = c(-10, 0))     # range of latitudes
#> <DataArray> '(unnamed)'
#>   Dimensions:  (lat: 2, lon: 4)
#>   Coordinates:
#>     * lat  (lat) -10 to 0
#>     * lon  (lon) 100 to 130
#>   dtype: integer  (32 B)

# Select by integer index
isel(da, lon = 1:2)          # first two longitude columns
#> <DataArray> '(unnamed)'
#>   Dimensions:  (lat: 3, lon: 2)
#>   Coordinates:
#>     * lat  (lat) -10 to 10
#>     * lon  (lon) 100 to 110
#>   dtype: integer  (24 B)
isel(da, lat = 2, lon = 3)   # single cell
#> <DataArray> '(unnamed)'
#>   dtype: integer  (4 B)