移动内核中两个矩阵中的最小单元格

Question

我有两个矩阵 m1 和 m2。

m1 <- matrix(1:16, ncol = 4)
m2 <- matrix(16:1, ncol = 4)
# > m1
# [,1] [,2] [,3] [,4]
# [1,]    1    5    9   13
# [2,]    2    6   10   14
# [3,]    3    7   11   15
# [4,]    4    8   12   16

# > m2
# [,1] [,2] [,3] [,4]
# [1,]   16   12    8    4
# [2,]   15   11    7    3
# [3,]   14   10    6    2
# [4,]   13    9    5    1

我想为 3x3 的移动内核中的每个单元格找到两个矩阵之间的最小值。应该忽略外边距，即它们可以用 NAs 填充，然后 min 函数应该有 na.rm = TRUE。结果应如下所示：

# > m3
#      [,1] [,2] [,3] [,4]
# [1,]    1    1    3    3
# [2,]    1    1    2    2
# [3,]    2    2    1    1
# [4,]    3    3    1    1

我已经尝试过 pmin{base} 和 runmin{caTools} 的组合，如下所示：

pmin(runmin(m1, 3, endrule = "keep"), 
     runmin(m2, 3, endrule = "keep"))

但是，这没有用。可能是因为

"If x is a matrix than each column will be processed separately." (from ?runmin)

是否有执行此类操作的软件包，或者是否可以 apply？

Answer 1

这是一个基础 R 方法：

m    = pmin(m1, m2)
grid = expand.grid(seq(nrow(m)), seq(ncol(m)))

x = apply(grid, 1, function(u) {
   min(m[max(1,u[1]-1):min(nrow(m), u[1]+1), max(1,u[2]-1):min(ncol(m), u[2]+1)])
})

dim(x) = dim(m)

#> x
#     [,1] [,2] [,3] [,4]
#[1,]    1    1    3    3
#[2,]    1    1    2    2
#[3,]    2    2    1    1
#[4,]    3    3    1    1

移动内核中两个矩阵中的最小单元格

Minimum of cells in two matrices within a moving kernel

r

matrix

cells