replace_single_square_bracket: Replace values of a GRaster

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

Replace values of a GRaster

Description

The ⁠[<-⁠ operator can be used to replace all of the values of a GRaster, or specific values depending on the expression in i. For example, you could use rast[] <- 10 to assign 10 to all cells, or rast[rast > 0] <- 10 to assign all cells with values >0 to 10. You can also use one raster to set values in another, as in rast1[rast2 > 0] <- 10.

Usage

## S4 replacement method for signature 'GRaster,missing,ANY'
x[i, j] <- value

## S4 replacement method for signature 'GRaster,GRaster,ANY'
x[i, j] <- value

Arguments

x	A GRaster.
i	Either missing or a conditional statement that resolves to a GRaster.
j	Not used
value	A numeric, integer, or logical value, or NA. Only a single value can be used.

Value

A GRaster.

Examples

if (grassStarted()) {

# Setup
library(terra)

### GRasters

# Example data
madElev <- fastData("madElev") # elevation raster
madForest2000 <- fastData("madForest2000") # forest raster
madForest2014 <- fastData("madForest2014") # forest raster

# Convert SpatRasters to GRasters
elev <- fast(madElev)
forest2000 <- fast(madForest2000)
forest2014 <- fast(madForest2014)

# Re-assigning values of a GRaster
constant <- elev
constant[] <- pi
names(constant) <- "pi_raster"
constant

# Re-assigning specific values of a raster
replace <- elev
replace[replace == 1] <- -20
replace

# Subsetting specific values of a raster based on another raster
elevInForest <- elev[forest2000 == 1]
plot(c(elev, forest2000, elevInForest), nr = 1)

# Adding and replacing layers of a GRaster
rasts <- c(elev, constant, forest2000)

# Combine with another layer:
add(rasts) <- forest2014 # one way
rasts

rasts <- c(rasts, forest2014) # another way

### Subsetting GRaster layers

# Subset:
rasts <- c(elev, forest2000, forest2014)
rasts[[2:3]]
subset(rasts, 2:3)
subset(rasts, c("madForest2000", "madElev"))
rasts[[c("madForest2000", "madElev")]]
rasts$madForest2000

# Get every other layer:
rasts[[c(FALSE, TRUE)]]

### Replacing layers of a GRaster

# Replace a layer
logElev <- log(elev)
names(logElev) <- "logElev"
rasts$madForest2014 <- logElev
rasts

# Replace a layer:
rasts[[3]] <- forest2000
rasts

### GVectors

# example data
madDypsis <- fastData("madDypsis") # vector of points

# Convert SpatVector to GVector
dypsis <- fast(madDypsis)

### Retrieving GVector columns

dypsis$species # Returns the column

dypsis[[c("year", "species")]] # Returns a GRaster with these columns
dypsis[ , c("year", "species")] # Same as above

### Subsetting GVector geometries

# Subset first three geometries
dypsis[1:3]
dypsis[1:3, "species"]

# Get geometries by data table condition
dypsis[dypsis$species == "Dypsis betsimisarakae"]

### (Re)assigning GVector column values

# New column
dypsis$pi <- pi

# Re-assign values
dypsis$pi <- "pie"

# Re-assign specific values
dypsis$institutionCode[dypsis$institutionCode == "MO"] <-
   "Missouri Botanical Garden"

}

adamlilith/fasterRaster documentation built on Dec. 21, 2024, 2:04 a.m.