从两列矩阵创建 sf 对象 [英] Create sf object from two-column matrix

问题描述

我有一个简单的两列矩阵，我想将其转换为 sf 对象，其中每一行指定一个点:

I have a simple two-column matrix that I want to convert to an sf object where each row specifies a point:

> set.seed(123);m=matrix(runif(10),ncol=2)
> m
          [,1]      [,2]
[1,] 0.2875775 0.0455565
[2,] 0.7883051 0.5281055
[3,] 0.4089769 0.8924190
[4,] 0.8830174 0.5514350
[5,] 0.9404673 0.4566147

最简单的方法行不通，因为 apply 将点重新组合成一个矩阵，而操作只是变成了一个非常慢的转置函数:

The naivest approach doesn't work, as apply mashes the points back together into a matrix and the operation just becomes a very slow transpose function:

> apply(m,1,st_point)
          [,1]      [,2]      [,3]      [,4]      [,5]
[1,] 0.2875775 0.7883051 0.4089769 0.8830174 0.9404673
[2,] 0.0455565 0.5281055 0.8924190 0.5514350 0.4566147

如果不进行显式循环，我能想到的最好的方法是这个怪物:

Best I can come up with without doing an explicit loop is this monster:

> st_sfc(lapply(data.frame(t(m)),st_point))
Geometry set for 5 features 
geometry type:  POINT
dimension:      XY
bbox:           xmin: 0.2875775 ymin: 0.0455565 xmax: 0.9404673 ymax: 0.892419
epsg (SRID):    NA
proj4string:    NA
POINT(0.287577520124614 0.0455564993899316)
POINT(0.788305135443807 0.528105488047004)
POINT(0.4089769218117 0.892419044394046)
POINT(0.883017404004931 0.551435014465824)
POINT(0.940467284293845 0.456614735303447)

另一种选择是通过 sp 对象，但我不想这样做.我也想要一个只在基础 R 中的解决方案，所以没有转换为 data.table 或 tbl 等.

The other option is to go via sp objects, but I don't want to do that. I'd also like a solution in base R only, so no conversion to data.table or tbl etc.

我是否只是缺少一个简单的 as(m,"sf") 函数或类似的函数?

Am I just missing a simple as(m,"sf") function or suchlike?

推荐答案

根据 sf 文档

m %>% 
  as.data.frame %>% 
  sf::st_as_sf(coords = c(1,2))

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