在栅格列表列表上执行循环

Question

需要解决方案,将非常感谢帮助.

在下面的代码中,我创建了三个栅格.然后我number在这个栅格上创建一个随机的点位置,我收到一个三个矩阵的列表,其中包含那些随机位置的坐标samples.然后,我将这些位置和样本栅格值接收samplevalues.

我想改变的是,我想创建一组100,150,200和250个随机点位置(numberv).因此,在生成这些位置并接收位置列表后,每个栅格将被采样length(numberv) 次数(在这种情况下为4次).因为我有三个栅格,所以我想得到一个列表,第一个元素包括从我的三个栅格中获得的采样值,每个采样100次,第二个栅格值每次采样150次,等等.列表将包含length(numberv)元素.然后我会使用这些位置来获取这些位置的栅格值.

我只用一个样本(使用了1个元素向量number)粘贴了一个简单案例的干净代码,希望它有所帮助.

y <- matrix(1:300,100,3)
mv <- c(1,2,3)
rep = 200

valuematrix <- vector("list",ncol(y))

for (i in 1:ncol(y)) {
        newmatrix <- replicate(rep,y[,i])
        valuematrix[[i]] <- newmatrix
}

library(sp)
library(raster)

rasters <- setNames(lapply(valuematrix, function(x) raster(x)), 
                    paste0('raster',1:length(mv)))

# Create a loop that will sample the rasters

library(dismo)

number = 100                        # current number for random sample points number
numberv = c(100,150,200,250)        # sample number vector i want to use

# samples below will hold only coordinate values:
samples <- setNames(lapply(rasters, function(x) randomPoints(raster(x), 
                                                             n=number)), 
                    paste0('sample',1:length(mv)))

samplevalues <- vector("list",ncol(y))

for (i in 1:ncol(y)) {
        samplevalues[[i]] <- data.frame(samples[[i]],extract(rasters[[i]],
                                                             samples[[i]]))
}

Answer 1

这有效吗？

# Function to sample using a given number (returns list of three)
sample.number <- function(x) {
  rps <- lapply(rasters, function(y) randomPoints(raster(y),n=x))
  setNames(rps,paste0('sample',1:length(mv)))
}

# Apply sample.number() to your numberv list
sample.set <- lapply(numberv,sample.number)

# Function to extract values from a given sample
sample.extract <- function(x) {
  lapply(1:length(x),function(y) data.frame(x[[y]],extract(rasters[[y]],x[[y]])))
}

# Apply sample.extract() to the set of samples (returns list of four lists)
sample.values <- lapply(sample.set,sample.extract)

# Access sample 1 of number 200
summary(sample.values[[3]][[1]])