如何识别数组中最大值的位置? [英] how to identify positions of max value in an array?

问题描述

我的数组是

x <- array(1:24, dim=c(3,4,3))

我的任务1是根据前两个维度找到最大值

My task 1 is to find the max value according to the first two dimensions

x.max <- apply(x,c(1,2), function(x) ifelse(all(is.na(x)), NA, max(x, na.rm = TRUE)))    

如果有NA数据 我的任务2是在第三维上找到最大值位置. 我尝试过

in case there is NA data my task 2 is to find the max value position on the third dimension. I tried

x.max.position = apply(x, c(1,2),which.max(x))

但这只给了我在拳头两个维度上的位置.

But this only give me the position on the fist two dimensions.

有人可以帮助我吗?

推荐答案

目前尚不完全清楚，但是如果您要为每个三维维度的矩阵找到max(那是技术上正确的说法吗? )，那么您需要在第三维中使用apply. ?apply下的参数margin指出:

It's not totally clear, but if you want to find the max for each matrix of the third dimension (is that even a technically right thing to say?), then you need to use apply across the third dimension. The argument margin under ?apply states that:

一个给出下标的向量，该函数将被应用到下标.例如，对于矩阵，1表示行，2表示列，c(1，2)表示行和列.

a vector giving the subscripts which the function will be applied over. E.g., for a matrix 1 indicates rows, 2 indicates columns, c(1, 2) indicates rows and columns.

因此，对于具有3D数组的示例，3是第三维.所以...

So for this example where you have a 3D array, 3 is the third dimension. So...

t( apply( x , 3 , function(x) which( x == max(x) , arr.ind = TRUE ) ) ) 
     [,1] [,2]
[1,]    3    4
[2,]    3    4
[3,]    3    4

这将返回一个矩阵，其中每行包含第三个维度的每个2D数组/矩阵的最大值的行和列索引.

Which returns a matrix where each row contains the row and then column index of the max value of each 2D array/matrix of the third dimension.

如果希望在所有维度上使用max，则可以使用which和arr.ind参数，如下所示:

If you want the max across all dimensions you can use which and the arr.ind argument like this:

which( x==max(x,na.rm=T) , arr.ind = T )
     dim1 dim2 dim3
[1,]    3    4    2

告诉我们max的值是第三行，第四列，第二个矩阵.

Which tells us the max value is the third row, fourth column, second matrix.

要找到第3点的位置，第1点和第2点的值最大，请尝试:

To find the position at dim 3 where where values on dim 1 and 2 are max try:

which.max( apply( x , 3 , max ) )
# [1] 2

告诉我们，三维的第2个位置包含最大值.

Which tells us that at position 2 of the third dimension contains the maximal value.

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