DataFrame转sf对象时geometry列异常的问题及解决方法

我的tibble数据中，geometry列意外变为字符串类型（存储为类似list(c(...))的文本格式），此时调用st_sf函数会报错：no simple features geometry column present。

数据预览如下：

> head(double_early_1995, 20)
# A tibble: 20 × 4
   yield pattern      year  geometry                                                                                               
   <dbl> <chr>        <chr> <chr>                                                                                                  
 1 4380. Double_Early 1995  list(c(117.2259, 117.2659, 117.2659, 117.2259, 117.2259, 31.5508, 31.5508, 31.5108, 31.5108, 31.5508))
 2 4691. Double_Early 1995  list(c(117.2659, 117.3059, 117.3059, 117.2659, 117.2659, 31.5508, 31.5508, 31.5108, 31.5108, 31.5508))
 3 3941. Double_Early 1995  list(c(117.3059, 117.3459, 117.3459, 117.3059, 117.3059, 31.5508, 31.5508, 31.5108, 31.5108, 31.5508))
 4 4286. Double_Early 1995  list(c(117.3459, 117.3859, 117.3859, 117.3459, 117.3459, 31.5508, 31.5508, 31.5108, 31.5108, 31.5508))
 5 4012. Double_Early 1995  list(c(117.1459, 117.1859, 117.1859, 117.1459, 117.1459, 31.5108, 31.5108, 31.4708, 31.4708, 31.5108))
 6 4413. Double_Early 1995  list(c(117.1859, 117.2259, 117.2259, 117.1859, 117.1859, 31.5108, 31.5108, 31.4708, 31.4708, 31.5108))
 7 3897. Double_Early 1995  list(c(117.2659, 117.3059, 117.3059, 117.2659, 117.2659, 31.5108, 31.5108, 31.4708, 31.4708, 31.5108))
 8 3857. Double_Early 1995  list(c(117.3059, 117.3459, 117.3459, 117.3059, 117.3059, 31.5108, 31.5108, 31.4708, 31.4708, 31.5108))
 9 3810. Double_Early 1995  list(c(117.3459, 117.3859, 117.3859, 117.3459, 117.3459, 31.5108, 31.5108, 31.4708, 31.4708, 31.5108))
10 3787. Double_Early 1995  list(c(117.3859, 117.4259, 117.4259, 117.3859, 117.3859, 31.5108, 31.5108, 31.4708, 31.4708, 31.5108))
11 3844. Double_Early 1995  list(c(117.9059, 117.9459, 117.9459, 117.9059, 117.9059, 31.5108, 31.5108, 31.4708, 31.4708, 31.5108))
12 4281. Double_Early 1995  list(c(117.0659, 117.1059, 117.1059, 117.0659, 117.0659, 31.4708, 31.4708, 31.4308, 31.4308, 31.4708))
13 3509. Double_Early 1995  list(c(117.1059, 117.1459, 117.1459, 117.1059, 117.1059, 31.4708, 31.4708, 31.4308, 31.4308, 31.4708))
14 3704. Double_Early 1995  list(c(117.1459, 117.1859, 117.1859, 117.1459, 117.1459, 31.4708, 31.4708, 31.4308, 31.4308, 31.4708))
15 4431. Double_Early 1995  list(c(117.1859, 117.2259, 117.2259, 117.1859, 117.1859, 31.4708, 31.4708, 31.4308, 31.4308, 31.4708))
16 4532. Double_Early 1995  list(c(117.2259, 117.2659, 117.2659, 117.2259, 117.2259, 31.4708, 31.4708, 31.4308, 31.4308, 31.4708))
17 3908. Double_Early 1995  list(c(117.2659, 117.3059, 117.3059, 117.2659, 117.2659, 31.4708, 31.4708, 31.4308, 31.4308, 31.4708))
18 3839. Double_Early 1995  list(c(117.3059, 117.3459, 117.3459, 117.3059, 117.3059, 31.4708, 31.4708, 31.4308, 31.4308, 31.4708))
19 3846. Double_Early 1995  list(c(117.3859, 117.4259, 117.4259, 117.3859, 117.3859, 31.4708, 31.4708, 31.4308, 31.4308, 31.4708))
20 3780. Double_Early 1995  list(c(117.4259, 117.4659, 117.4659, 117.4259, 117.4259, 31.4708, 31.4708, 31.4308, 31.4308, 31.4708))

解决方法 #

通过字符串解析将geometry列转换为sfc类型，具体代码如下：

double_early_1995 <- double_early_1995 %>%
  mutate(geometry = st_sfc(lapply(geometry, 
                                  function(coords) { st_polygon(list(matrix(as.numeric(unlist(strsplit(substr(coords, 8, (nchar(coords) - 2)), ", "))), 
                                                                            ncol = 2, byrow = F)))}))) 

代码逻辑说明：

• substr(coords, 8, (nchar(coords) - 2))：去除字符串开头的list(c(和结尾的))，提取纯坐标文本
• strsplit(..., ", ")：按逗号分割坐标文本为单个字符串元素
• unlist() + as.numeric()：将分割后的列表转为数值型向量
• matrix(..., ncol=2, byrow=F)：将数值向量转为2列矩阵（对应经度、纬度）
• st_polygon(list(...))：将矩阵转为多边形几何对象
• lapply() + st_sfc()：对每行geometry文本执行转换，最终生成sfc类型的几何列

内容的提问来源于stack exchange，提问作者Yabin Da