match: Find which cells of a GRaster match certain values

In adamlilith/fasterRaster: Faster Raster and Spatial Vector Processing Using 'GRASS GIS'

Find which cells of a GRaster match certain values

Description

The match() function takes a GRaster and a numeric, integer or character vector as inputs and returns a GRaster with cell values that correspond to the index of each element in the vector that matched the original cell value. For example, if a 4-cell raster had values 3, NA, 5, 4, and the vector was c(3, 4), then the output would be a 4-cell raster with values 1, NA, NA, 2 because the first value in the vector was 3 (so the cell with 3 is assigned 1), and because the second value in the vector was 4 (so the cell with 4 was assigned 2). The other two values had no matches.

If the GRaster is categorical, then the vector can be category labels instead of numeric values.

The %in% operator returns a GRaster with cell values that are 1 if their original values appeared in the vector, and 0 if not (or NA if the original value was NA). If the GRaster is categorical, then the vector can be category labels instead of numeric values.

The ⁠%notin%⁠ operator returns 1 for cells with values that are not found in the vector, and 0 otherwise. If the GRaster is categorical, then the vector can be category labels instead of numeric values.

Usage

## S4 method for signature 'GRaster'
match(x, table, nomatch = NA)

## S4 method for signature 'GRaster'
x %in% table

## S4 method for signature 'GRaster'
x %notin% table

Arguments

x	A GRaster: Note that any kind of GRaster is acceptable (integer, float, double, or categorical), but matching may not work as intended for float and double rasters because of problems with comparing floating-point values.
table	A numeric, integer, or character vector.
nomatch	Numeric or integer: Value to return when no match is found.

Value

A GRaster.

See Also

terra::match(), match(), omnibus::notIn()

Examples

if (grassStarted()) {

# Setup
library(terra)

# Example data: Elevation and land cover rasters
madElev <- fastData("madElev")
madCover <- fastData("madCover")

### match() with an integer raster:
###################################

elev <- fast(madElev)

# Cells in elevation raster replaced with index in which they appear
# in the table:
table <- c(10, 20, 30, 40, 50)
elevIndex <- match(elev, table)
elevIndexNeg <- match(elev, table, nomatch = -100)

plot(c(elevIndex, elevIndexNeg))

### Using %in% and %notin% on an integer GRaster:
#################################################

elev <- fast(madElev)
table <- c(10, 20, 30, 40, 50)

ins <- elev %in% table
notins <- elev %notin% table

plot(c(ins, notins))

### match() with a categorical raster:
######################################

cover <- fast(madCover)
cover <- droplevels(cover)
levels(cover)

forestLabels <- c(
   "Sparse broadleaved evergreen/semi-deciduous forest",
   "Broadleaved deciduous forest",
   "Grassland with mosaic forest",
   "Flooded forest"
)

forestClasses <- match(cover, forestLabels)
plot(forestClasses)
levels(forestClasses)

forestNoMatch <- match(cover, forestLabels, nomatch = -100)
plot(forestNoMatch)
levels(forestNoMatch)

### Using %in% and %notin% on a categorical GRaster:
####################################################

cover <- fast(madCover)
cover <- droplevels(cover)
levels(cover)

forestLabels <- c(
   "Sparse broadleaved evergreen/semi-deciduous forest",
   "Broadleaved deciduous forest",
   "Grassland with mosaic forest",
   "Flooded forest"
)

forest <- cover %in% forestLabels
plot(forest)

notForest <- cover %notin% forestLabels
plot(notForest)

}

adamlilith/fasterRaster documentation built on Oct. 26, 2024, 4:06 p.m.