# Subset a GRaster layer, or return values from a column of a GVector's table The `dollar` notation can be used to get a single layer of a multi-layer `GRaster` or the values of a column from a `GVector`'s data table. methods ```r ## S4 method for signature 'GRaster' x$name ## S4 method for signature 'GVector' x$name ``` ## Arguments - `x`: A `GRaster` or `GVector`. - `name`: Character: The name of a `GRaster` or of a column of a `GVector`'s data table. Names of rasters and vectors can be found using `names()`. ## Returns A `GRaster` or vector of the same type as the `GVector`'s column. ## Examples ```r 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 madDypsis <- vect(madDypsis) # Convert SpatVector to GVector dypsis <- fast(madDypsis) ### Retrieving GVector columns dypsis$species # Returns the column dypsis[[c("year", "species")]] # Returns a GVector with these columns dypsis[ , c("year", "species")] # Same as above ### Subsetting GVector geometries # Subset three geometries dypsis[c(1, 4, 10)] # Subset three geometries and one column. Note order will always be the same # in the output and may differ in order from terra subsetting. dypsis[c(1, 4, 10), "species"] dypsis[c(10, 4, 1), "species"] # fasterRaster: Same order as previous. madDypsis[c(1, 4, 10), "species"] madDypsis[c(10, 4, 1), "species"] # terra: different order as previous. # Get geometries by data table condition dypsis[dypsis$species == "Dypsis betsimisarakae"] ### (Re)assigning GVector column values # New column dypsis$pi <- pi head(dypsis) # Re-assign values dypsis$pi <- "pie" head(dypsis) # Re-assign specific values dypsis$institutionCode[dypsis$institutionCode == "MO"] <- "Missouri Botanical Garden" } ``` ## See Also `subset()`, `[`, `[[`

subset_dollar function