R - 在数组维度中找到唯一的最小值

Question

在 4 维数组中，我想找到第 4 维的唯一最小值。我想获得最小值的数组索引矩阵。

我已尝试使用以下代码块解决问题。我本来喜欢使用 which.min，但我还没有找到 return 数组索引的好方法。

dims =c(3,3,3,4)

# create sample data with multiple mins in [,,,1]
mat_rep = array(c(rep(0,3),sample(1:prod(dims))), dim = dims)
pos_rep = apply(mat_rep, 4, function(x) which(x == min(x), arr.ind = T)) # get position of unique minimum 

# create sample data with unique min
mat_norep = array(sample(1:prod(dims)), dim = dims)
pos_norep = apply(mat_norep, 4, function(x) which(x == min(x), arr.ind = T))

# formating depending on class of pos_ object
format_pos = function(x, dims){
  if(class(x) == "matrix") x = t(x)
  if(class(x) == "list") x = do.call(rbind, lapply(x, head, 1))
  x = cbind(x, 1:dims[4]) # add 4th dimension
  return(x)
}

format_pos(pos_norep, dims = dims)
format_pos(pos_rep, dims = dims)

所描述的解决方案有效，但它通常不起作用，我认为 if(class()) 和 cbind(x, 1:dims[4]) 容易产生错误。有人有更简洁的方法来解决这个问题吗？

Answer 1

要创建统一输出，您可以在 apply(..., which.min) 的输出上显式调用 arrayInd，而不是像 which(..., arr.ind = TRUE) 中那样隐式调用。第四维度索引仍然需要手动添加：

## add 4D indices using 1D values
start.ind <- (seq_len(dims[4]) - 1) * prod(head(dims, 3))

arrayInd(apply(mat_rep, 4, which.min) + start.ind, .dim = dims)
#>      [,1] [,2] [,3] [,4]
#> [1,]    1    1    1    1
#> [2,]    1    3    3    2
#> [3,]    1    3    2    3
#> [4,]    3    1    1    4
arrayInd(apply(mat_norep, 4, which.min) + start.ind, .dim = dims)
#>      [,1] [,2] [,3] [,4]
#> [1,]    2    1    3    1
#> [2,]    1    2    1    2
#> [3,]    1    2    1    3
#> [4,]    2    2    3    4

## add 4D indices using cbind
cbind(arrayInd(apply(mat_rep, 4, which.min), .dim = head(dims, 3)), seq_len(dims[4]))
#>      [,1] [,2] [,3] [,4]
#> [1,]    1    1    1    1
#> [2,]    1    3    3    2
#> [3,]    1    3    2    3
#> [4,]    3    1    1    4

cbind(arrayInd(apply(mat_norep, 4, which.min), .dim = head(dims, 3)), seq_len(dims[4]))
#>      [,1] [,2] [,3] [,4]
#> [1,]    2    1    3    1
#> [2,]    1    2    1    2
#> [3,]    1    2    1    3
#> [4,]    2    2    3    4

数据

dims <- c(3,3,3,4)
mat_rep <- array(c(rep(0,3),sample(1:prod(dims))), dim = dims)
mat_norep <- array(sample(1:prod(dims)), dim = dims)

R - 在数组维度中找到唯一的最小值

R - Find unique minimum across array dimension

arrays

r

min