将强化的data.frame转换回sf对象 [英] convert a fortified data.frame back to sf object

问题描述

fiftystater软件包提供了一张包含夏威夷和阿拉斯加的美国详细地图，如下所示.对象五十状态已被强化，可与ggplot2一起使用.但是，我想使用geom_sf将其绘制为一个sf对象.

fiftystater package provides a great map of USA that has Hawaii and Alaska as insets below. The object fifty_states comes already fortified for use with ggplot2. However, I would like to plot this as an sf object using geom_sf.

作为一个更普遍的问题，将强化的data.frame转换回SF多边形的最佳方法是什么?

As a more general question, what is the best way to convert a fortified data.frame back into sf polygon?

library(fiftystater)
fifty_states <– fifty_states

> head(fifty_states)
       long      lat order  hole piece      id     group
1 -85.07007 31.98070     1 FALSE     1 alabama Alabama.1
2 -85.11515 31.90742     2 FALSE     1 alabama Alabama.1
3 -85.13557 31.85488     3 FALSE     1 alabama Alabama.1
4 -85.13156 31.78381     4 FALSE     1 alabama Alabama.1
5 -85.13017 31.77885     5 FALSE     1 alabama Alabama.1
6 -85.11529 31.73157     6 FALSE     1 alabama Alabama.1

请注意此问题来自坐标的多边形有点相似，但不能完全满足我的需要

note this question polygons from coordinates is kind of similar but doesn't quite do what I need.

推荐答案

这将起作用:首先使用st_as_sf转换为点sf数据集，然后根据每个状态/块的点创建多边形.

this would work: you first convert to a point sf dataset using st_as_sf, and then create polygons from the points of each state/piece.

sf_fifty <- sf::st_as_sf(fifty_states, coords = c("long", "lat")) %>% 
  group_by(id, piece) %>% 
  summarize(do_union=FALSE) %>%
  st_cast("POLYGON") %>% 
  ungroup()

plot(sf_fifty["id"])

(另请参见 https://github.com/r-spatial/sf/issues /321 )

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