[英]Distance to nearest point by group using sf
I have a dataset that looks similar to the example below. 我有一个看起来与下面的示例相似的数据集。 For each
code
I would like to calculate the distance to the next nearest code that belongs to the same area
as it. 对于每个
code
我想计算到与它属于同一area
的下一个最近代码的距离。 So in my example, for each code belonging to area A001 I would be after an additional column in the dataset that contains the minimum distance to one of the other points that belong to area A001. 因此,在我的示例中,对于属于区域A001的每个代码,我将在数据集中的另一列之后,该列包含与属于区域A001的其他点之一的最小距离。 I assume there should be a way of using
st_distance
to achieve this? 我认为应该有一种使用
st_distance
来实现这一目标?
require("data.table")
require("sf")
dt1 <- data.table(
code=c("A00111", "A00112","A00113","A00211","A00212","A00213","A00214","A00311","A00312"),
area=c("A001", "A001","A001","A002","A002","A002","A002","A003","A003"),
x=c(325147,323095,596020,257409,241206,248371,261076,595218,596678),
y=c(286151,284740,335814,079727,084266,078283,062045,333889,337836))
sf1 <- st_as_sf(dt1, coords = c("x","y"), crs=27700, na.fail=FALSE)
There might be a 'cleaner' way to get here, but this gets you the correct values. 到达这里可能会有一种“更清洁”的方法,但这可以为您提供正确的值。
library(tidyverse)
# intermediate fun to help later in apply()
smallest_non_zero <- function(x) {
min_val <- min(x[x != 0])
x[match(min_val, x)]
}
closest_grp_distances <- sf1 %>%
group_split(area) %>%
map(~st_distance(., .) %>% # returns matrix
apply(1, smallest_non_zero)) %>%
unlist()
sf1$closest_grp_distances <- closest_grp_distances
I wanted to use the baseR split
but it doesn't have a method for sf
objects. 我想使用baseR
split
但是它没有用于sf
对象的方法。
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