如何使用类别名称对 terra 中的分类栅格进行重新分类

Question

我希望能够合并分类栅格中的两个类别。到目前为止我找到的唯一解决方案使用级别索引号，而不是类别名称。我如何使用类别名称来做到这一点？

library(terra)
m <- matrix(rep(c("a", "b", "c"), each = 3), nrow = 3, ncol = 3)
x <- rast(m)

x[x$lyr.1 == "c"]

m2 <- matrix(c("a", "a", "b", "b", "c", "b"), nrow = 3, ncol = 2, byrow = TRUE)

test <- classify(x, m2)
#doesn't work with category names

test <- subst(x, "c", "b")
#doesn't work with category names

test <- subst(x, 2, 1)
#works with category index

Answer 1

示例数据

library(terra)
m <- matrix(rep(c("a", "b", "c"), each = 3), nrow = 3, ncol = 3)
x <- rast(m)
m2 <- matrix(c("a", "a", "b", "b", "c", "b"), nrow = 3, ncol = 2, byrow = TRUE)

对于当前版本的 terra，您可以执行以下任一

test1 <- subst(x, "c", "b")

操作：

test2 <- subst(x, 2, 1, raw=TRUE)

Answer 2

library(terra)
library(tidyverse)

m <- matrix(rep(c("a", "b", "c"), each = 3), nrow = 3, ncol = 3)
x <- rast(m)

plot(x)

reclassified <- cats(x)[[1]] %>%
  mutate(label_reclass = forcats::fct_collapse(cats(x)[[1]]$label,c="b"))

x <- categories(x, layer=1, value=reclassified, active=2)

图(x)

levels(x)

[[1]]
  value label_reclass
1     1             a
2     2             c
3     3             c