Question

我的数据框包含Name，longitude和latitude列。我想要一个遍历每一行的函数，从栅格堆栈中提取值并根据Name列编写csv文件。

Name    Lon     Lat
Name1   11.11   47.87
Name2   150.1   -40.4
Name3   -50.2   -3.5
Name4   -100.3  49.8

library(raster)
s <- stack(replicate(5, {raster(matrix(runif(2160*4320), 2160), 
         xmn=-180, xmx=180, ymn=-90, ymx=90)}))

I can do that one by one:

location <- data.frame(11.11, 47.87)
ex <- extract(s, location)
write.csv(ex, "Name1.csv")

Answer 1

一种非常传统的方法适用于for-loop

d1 <-c("Name1", "Name2","Name3", "Name4")
d2 <- c(11.11,150.1,-50.2,-100.3)
d3 <-c(47.87, -40.4, -3.5, 49.8)
data.df <-data.frame(d1,d2,d3)

for(i in 1:nrow(data.df)) 
{
  location <- data.frame(data.df[i,2],data.df[,3])
  ex <- extract(s, location)
  fn1<-paste0(data.df[i,1],".csv")
  write.csv(ex, fn1)
}

生成四个包含以下信息的文件：

"","layer.1","layer.2","layer.3","layer.4","layer.5"
"1",0.471816286211833,0.115963410818949,0.399704266572371,0.464667820138857,0.820669727399945
"2",0.616754011251032,0.354018000885844,0.602565947687253,0.86519843316637,0.660861984360963
"3",0.0691961287520826,0.128835600335151,0.199198298621923,0.968016018159688,0.597145217470825

我希望这是您正在寻找的结果。可能有一些更先进和更好的方法（基于apply - 家庭???）和作为R初学者也感兴趣。

Answer 2

申请：

library(raster)
s <- stack(replicate(5, {raster(matrix(runif(2160*4320), 2160), 
                                xmn=-180, xmx=180, ymn=-90, ymx=90)}))

d1 <-c("Name1", "Name2","Name3", "Name4")
d2 <- c(11.11,150.1,-50.2,-100.3)
d3 <-c(47.87, -40.4, -3.5, 49.8)
data.df <- data.frame("Name" = d1, "Lon" = d2, "Lat" = d3)

apply(X = data.df, 1, function(x, s) {
        location <- as.numeric(c(x[2], x[3]))
        ex <- extract(s, location)
        write.csv(ex, paste0(x[1], ".csv"))
}, s = s)

请注意，如果要在函数内部使用，则必须将s对象作为函数的附加参数传递。

遍历数据框中的每一行，从栅格中提取值并写入csv文件

2 个答案: