R语言terra包，extract 从SpatRaster中提取值
# Wed Dec 16 14:02:09 2020 -
# 字符编码：UTF-8
# R 版本：R x64 4.0.3 for window 10
# cgh163email@163.com
# 个人笔记不负责任
# —— 拎了个梨🍐
.rs.restartR()
require(terra)
# extract 从SpatRaster中提取值
rm(list=ls());gc()
r <- rast(ncol=5, nrow=5, xmin=0, xmax=5, ymin=0, ymax=5)
values(r) <- 1:25
xy <- rbind(c(0.5,0.5), c(2.5,2.5))
p <- vect(xy, crs="+proj=longlat +datum=WGS84")
extract(r, xy)
extract(r, p)
r[1,]
r[5]
r[,5]
r[c(0:2, 99:101)]
f <- system.file("ex/test.tif", package="terra")
r <- rast(f)
xy <- cbind(179000, 330000)
xy <- rbind(xy-100, xy, xy+1000)
extract(r, xy)
p <- vect(xy)
g <- geom(p)
g
extract(r, p)
x <- r + 10
extract(x, p)
i <- cellFromXY(r, xy)
x[i]
r[i]
y <- c(x,x*2,x*3)
y[i]
## extract with a polygon
#f <- system.file("ex/lux.shp", package="terra")
#v <- vect(f)
#z <- rast(v)
#v <- v[1:2,]
#values(z) <- 1:100
#e <- extract(z, v)
#e
#tapply(e[,2], e[,1], mean)
#ee <- extract(z, v, list=TRUE)
#rapply(ee, mean)
#x <- c(z, z*2, z/3)
#names(x) <- letters[1:3]
#e <- extract(x, v)
#de <- data.frame(e)
#aggregate(de[,2:4], de[,1,drop=FALSE], mean)
#ee <- extract(x, v, list=TRUE)
#matrix(rapply(ee, mean), ncol=nlyr(x), byrow=TRUE)
