R：将data.frames列表转换为栅格列表

Let's say I have a list of data.frames:

假设我有一个data.frames列表：

a1<-as.data.frame(1:9)
a2<-as.data.frame(2:10)
a3<-as.data.frame(3:11)

a.list<-list(a1,a2,a3)

Now I want to convert each data.frame of the list into a 3 by 3 raster layer. The layers should be in a list afterwards.

现在我想将列表的每个data.frame转换为3乘3的栅格图层。之后，图层应该在列表中。

I tried to perform this with lapply, but can't really tell what the problem is:

我尝试用lapply执行此操作，但无法确定问题是什么：

r.list<-lapply(a.list, raster(nrows=3, ncols=3))

2 个解决方案

#1

You probably need to convert your dataframes to matrices first. Exploit the fact that you have 1-column data frames to convert them to vectors and then use the matrix function:

您可能需要先将数据帧转换为矩阵。利用以下事实：您有1列数据帧将它们转换为向量，然后使用矩阵函数：

> rl = lapply(a.list, function(X) raster(matrix(X[,1],nrow=3)))
> rl[[1]]
class       : RasterLayer 
dimensions  : 3, 3, 9  (nrow, ncol, ncell)
resolution  : 0.3333333, 0.3333333  (x, y)
extent      : 0, 1, 0, 1  (xmin, xmax, ymin, ymax)
coord. ref. : NA 
data source : in memory
names       : layer 
values      : 1, 9  (min, max)

You may want to make sure the rasters are being constructed row-wise or column-wise - use the byrow arg to matrix to adjust this, or transpose the matrix or otherwise arrange it.

您可能希望确保栅格是按行或逐列构建的 - 使用byrow arg to matrix来调整它，或者转置矩阵或以其他方式排列它。

#2

Your problem is that you're trying to convert nrows=3 into a raster object, and then apply that new object as a function operating on each element of a.list.

您的问题是您正在尝试将nrows = 3转换为栅格对象，然后将该新对象应用为对a.list的每个元素进行操作的函数。

You want either:

你想要：

lapply(a.list, raster, nrows=3, ncols=3)

Or:

要么：

lapply(a.list, function(X) raster(X, nrows=3, ncols=3))

#1