R 基于光栅的快速复制随机采样

我必须对光栅中每个网格多边形的一个点进行随机采样，迭代1000次，网格大小从5到25。 对于光栅50 x 50（2500个单元），该过程需要1小时以上，代码如下：

library(raster)
library(dplyr)

# This is the script for random sampling inside the grid cells
sample_grid <- function(r, w, n){

  grid <- raster(extent(r))
  res(grid) <- w
  proj4string(grid) <- proj4string(r)
  gridpolygon <- rasterToPolygons(grid)

  pickpts <- sapply(gridpolygon@polygons, spsample, n = n, type = "random")
  sapply(pickpts, FUN = extract, x = r)
}

# Let's make a raster
r <- raster(ncol = 50, nrow = 50, xmn = 0, xmx = 50, ymn = 0, ymx = 50)
values(r) <- runif(ncell(r))

# Repeat the random sampling process 1000 times for different grid sizes
sapply(5:25, function(x) replicate(1000, sample_grid(r, x, 1) %>% 
                                               mean(., na.rm = TRUE)))

---

看起来可以在相同的

sapply

调用中完成

sample\u grid

中的最后两个步骤。你分析过这个函数了吗？我添加了

summaryRprof

的输出。

Rprof(tmp <- tempfile())
sample_grid(r, 10, 1) %>% mean(., na.rm = TRUE)
Rprof()
summaryRprof(tmp)

#################### summaryRprof output ####################
$by.self
                     self.time self.pct total.time total.pct
"eval"                    0.02    14.29       0.14    100.00
"initialize"              0.02    14.29       0.06     42.86
"getClassDef"             0.02    14.29       0.04     28.57
".getClassFromCache"      0.02    14.29       0.02     14.29
"aperm"                   0.02    14.29       0.02     14.29
"merge.data.frame"        0.02    14.29       0.02     14.29
"validityMethod"          0.02    14.29       0.02     14.29

$by.total
                      total.time total.pct self.time self.pct
"eval"                     0.14    100.00      0.02    14.29
"%>%"                      0.14    100.00      0.00     0.00
".local"                   0.14    100.00      0.00     0.00
"FUN"                      0.14    100.00      0.00     0.00
"lapply"                   0.14    100.00      0.00     0.00
"sample_grid"              0.14    100.00      0.00     0.00
"sapply"                   0.14    100.00      0.00     0.00
"standardGeneric"          0.14    100.00      0.00     0.00
"initialize"               0.06     42.86      0.02    14.29
"new"                      0.06     42.86      0.00     0.00
"getClassDef"              0.04     28.57      0.02    14.29
".cellValues"              0.04     28.57      0.00     0.00
".readCells"               0.04     28.57      0.00     0.00
".xyValues"                0.04     28.57      0.00     0.00
"CRS"                      0.04     28.57      0.00     0.00
"over"                     0.04     28.57      0.00     0.00
"sample.Polygon"           0.04     28.57      0.00     0.00
"validObject"              0.04     28.57      0.00     0.00
".getClassFromCache"       0.02     14.29      0.02    14.29
"aperm"                    0.02     14.29      0.02    14.29
"merge.data.frame"         0.02     14.29      0.02    14.29
"validityMethod"           0.02     14.29      0.02    14.29
".bboxCoords"              0.02     14.29      0.00     0.00
".uniqueNames"             0.02     14.29      0.00     0.00
"["                        0.02     14.29      0.00     0.00
"anyStrings"               0.02     14.29      0.00     0.00
"apply"                    0.02     14.29      0.00     0.00
"as.matrix"                0.02     14.29      0.00     0.00
"identical"                0.02     14.29      0.00     0.00
"identicalCRS"             0.02     14.29      0.00     0.00
"is"                       0.02     14.29      0.00     0.00
"match.arg"                0.02     14.29      0.00     0.00
"merge"                    0.02     14.29      0.00     0.00
"merge.default"            0.02     14.29      0.00     0.00
"names"                    0.02     14.29      0.00     0.00
"SpatialPolygons"          0.02     14.29      0.00     0.00
"stopifnot"                0.02     14.29      0.00     0.00
"t"                        0.02     14.29      0.00     0.00
"table"                    0.02     14.29      0.00     0.00
"validNames"               0.02     14.29      0.00     0.00

$sample.interval
[1] 0.02

$sampling.time
[1] 0.14
###############################################################