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Reduction over named dims.

reduce_over.Rd

op is a reduction name, not a function: the planner needs op identity for algebraic decomposition and dtype rules. nan_rm = TRUE (the default) skips nodata, matching R's na.rm = TRUE under the NaN nodata sentinel. A pixel that is nodata in every input stays nodata (NaN) for "mean", "median", "min" and "max"; "sum" gives 0 and "count" gives 0. (The g_min() / g_max() primitives return their identity, Inf / -Inf, instead.)

Usage

reduce_over(x, op, over, nan_rm = TRUE, bands = NULL)

Arguments

x

A LazyRaster, or a LazyDataset.

op

Reduction name: one of "sum", "mean", "min", "max", "median", "count". Alternatively a custom reducer: a function fn(x, dims) written in the g_* vocabulary that collapses the margins dims (e.g. a per-pixel model fit over time).

over

Names of dims to reduce over (subset of names(dims)).

nan_rm

Skip NaN (nodata) values?

bands

LazyDataset only: bands to reduce (default: all bands).

Value

A LazyRaster on the reduced grid, or a LazyDataset when given one.

Details

Over a LazyDataset, each band is reduced independently (over "t": stack the band's slices and collapse time to a composite); bands restricts which bands. over = "band" collapses the band axis, returning a LazyRaster.

See also

geomedian() and medoid() for multivariate time composites; band_project() and mlp_project() for band-axis models; group_by_time() for calendar-grouped reduction; scan_over() for order-preserving passes.

Examples

f <- system.file("extdata", "garry-example.tif", package = "garry")
red <- lazy_source(f, band = 1L)
collect(reduce_over(red, "mean", c("x", "y")))
#> Error in confirm_plugin_install(platform, url): The "cpu" PJRT plugin needs to be downloaded for pjrt to work.
#> ℹ Automatic downloads are not performed in non-interactive sessions.
#> ℹ Set `PJRT_INSTALL` to "1" to allow the download, or set
#>   `PJRT_PLUGIN_PATH_CPU` to a local plugin file.
stk <- lazy_stack(list(a = red, b = red * 2))
dim(collect(reduce_over(stk, "median", "t")))
#> Error in confirm_plugin_install(platform, url): The "cpu" PJRT plugin needs to be downloaded for pjrt to work.
#> ℹ Automatic downloads are not performed in non-interactive sessions.
#> ℹ Set `PJRT_INSTALL` to "1" to allow the download, or set
#>   `PJRT_PLUGIN_PATH_CPU` to a local plugin file.