[英]Two lists in apply family
I am trying to extract two regions ex1
and ex2
(in exlist
) from a list of rasters ( rasterlist
) using the apply
family and extract
from the raster package.我正在尝试使用
apply
系列从栅格列表( rasterlist
)中提取两个区域ex1
和ex2
(在exlist
)并从栅格包中extract
。 I could use a nested for loop but was wondering if there is a way to achieve this in with one of the apply family members, since nested for loops are considered more or less bad practice in R .我可以使用嵌套的 for 循环,但想知道是否有一种方法可以使用 apply 家族成员之一来实现这一点,因为嵌套的 for 循环在 R 中或多或少被认为是不好的做法。 Here the dummy code:
这里是虚拟代码:
library(raster)
ras1 <- raster(matrix(runif(20), nrow = 5, ncol = 5))
ras2 <- ras1 * 2
ras3 <- ras1 * 0.5
rasterlist <- list(ras1, ras2, ras3)
ex1 <- extent(0, 0.4, 0, 0.4)
ex2 <- extent(0.6, 1, 0.4, 1)
exlist <- list(ex1, ex2)
At the moment I've got this as a (rather unsatisfying) solution:目前,我将此作为(相当不满意的)解决方案:
out1 <- lapply(rasterlist, function(i) extract(i, ex1))
out2 <- lapply(rasterlist, function(i) extract(i, ex2))
NB The solution it does not need to be a member of the apply family (although that was the task I set myself) if there is a better, faster, more elegant way please share.注:该解决方案并不需要是申请家庭成员(虽然这是我给自己定下任务)如果有一个更好,更快,更优雅的方式,请分享。
You could start with combining the regions into a single SpatialPolygons object (maybe they are to begin with?).您可以从将这些区域组合成一个 SpatialPolygons 对象开始(也许它们是从开始的?)。 With your example data that can be done like this:
使用可以像这样完成的示例数据:
ex <- do.call(bind, sapply(exlist, function(x) as(x, 'SpatialPolygons')))
In this example (with RasterLayer objects that can be stacked) you can then do在此示例中(使用可以堆叠的 RasterLayer 对象),您可以执行以下操作
s <- stack(rasterlist)
extract(s, ex)
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