R sf::st_convex_hull()在具有多个组的数据上丢失了sf类

Question

R sf::st_convex_hull()在具有多个组的数据上丢失了sf类

3

我正在尝试使用R中的sf包创建一个95％最小凸多边形。只要我只对一个变量分组，我的代码就能正常工作，但是当我对两个变量进行分组时，输出会失去其sf类并变成grouped_df。

这里是一个玩具数据集作为示例：

library(dplyr) 
set.seed(12)
toy <- tibble::tibble(
    ID = rep(c(1,2), each = 10),
    year = rep(c(1,2), 10),
    lat = runif(20, 1, 10),
    long = runif(20, 1, 10)
  ) %>%
    sf::st_as_sf(., coords = c("long", "lat")) 
toy %>%
  group_by(ID) %>% 
  summarize(.groups = "keep") %>% 
  mutate(cent = sf::st_centroid(geometry)) %>%
  sf::st_cast(to = "POINT") %>%  
  mutate(dist = sf::st_distance(geometry, cent, by_element = TRUE)) %>% 
  filter(dist <= quantile(dist, .95)) %>% 
  summarize()  %>%
  sf::st_convex_hull() %>%
  class()

这个代码可以输出我想要的结果。但是当我尝试按两个变量进行分组时，结果会丢失sf类。

toy %>%
  group_by(ID, year) %>% 
  summarize(.groups = "keep") %>% 
  mutate(cent = sf::st_centroid(geometry)) %>%
  sf::st_cast(to = "POINT") %>%  
  mutate(dist = sf::st_distance(geometry, cent, by_element = TRUE)) %>% 
  filter(dist <= quantile(dist, .95)) %>% 
  summarize()  %>%
  sf::st_convex_hull() %>%
  class

我的代码中是否有什么问题导致我无法按两个变量进行分组？

- anna

1个回答

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- at80 · Accepted Answer

这是因为第二个汇总正在ID上重新分组。您需要在那里添加 .groups = "keeps" 以通过相同的分组，然后将其转换回sf对象。或者，您可以创建一个分组变量 mutate（grp = paste0（ID，year）） 并执行 group_by（grp）。

toy %>%
  group_by(ID, year) %>% 
  summarize(.groups = "keep") %>% 
  mutate(cent = sf::st_centroid(geometry)) %>%
  sf::st_cast(to = "POINT") %>%  
  mutate(dist = sf::st_distance(geometry, cent, by_element = TRUE)) %>% 
  filter(dist <= quantile(dist, .95)) %>% 
  summarize(.groups = "keep")  %>%
  sf::st_convex_hull() %>%
  st_sf()