r - R中的滑动窗口函数

Question

有人知道 R 中是否有针对 2d 矩阵而不仅仅是向量的滑动窗口方法。我需要将中值函数应用于存储在矩阵中的图像

Answer 1

优秀的raster包中的函数focal()对此很有用。除了下面示例中显示的参数之外，它还需要几个参数，并且可以在需要时用于指定非矩形滑动窗口。

library(raster)

## Create some example data
m <- matrix(1, ncol=10, nrow=10)
diag(m) <- 2
r <- as(m, "RasterLayer") # Coerce matrix to RasterLayer object

## Apply a function that returns a single value when passed values of cells
## in a 3-by-3 window surrounding each focal cell 
rmean <- focal(r, w=matrix(1/9, ncol=3, nrow=3), fun=mean)
rmedian <- focal(r, w=matrix(1/9, ncol=3, nrow=3), fun=median)

## Plot the results to confirm that this behaves as you'd expect
par(mfcol=c(1,3))
plot(r)
plot(rmean)
plot(rmedian)

## Coerce results back to a matrix, if you so desire
mmean <- as(rmean, "matrix")