subset_single_bracket: Subset geometries of a GVector

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

Subset geometries of a GVector

Description

The [ operator returns a subset or remove specific geometries of a GVector. You can get the number of geometries using ngeom(). Note that you cannot use this function to change the "order" in which geometries or their associated records in a data table appear. For example, vector[1:3] and vector[3:1] will yield the exact same results.

Note that subsetting can take a very long time if you are retaining only a small number of geometries from a vector with many geometries. The routine selects geometries by removing those that are not in i. So if you can write code to remove fewer geometries (i.e., an "inverse" selection), it may go faster.

Usage

## S4 method for signature 'GVector,ANY,ANY'
x[i, j]

## S4 method for signature 'GRaster,GRaster,ANY'
x[i, j]

Arguments

x	A GVector.
i	Numeric integer, integer, or logical vector: Indicates which geometry(ies) to obtain. Negative numeric or integer values will remove the given geometries from the output. If a logical vector is supplied and it is not the same length as the number of geometries, it will be recycled.
j	Numeric integer, integer, logical, or character: Indices or name(s) of the column(s) to obtain. You can see column names using names(). Negative numeric or integer values will remove the given columns from the output. If a logical vector is supplied and it is not the same length as the number of columns, it will be recycled.

Value

A GVector.

See Also

subset(), $, [[

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.