获得R中矩阵的每行中K个最小或最大元素的索引

How to get indices of K smallest or largest elements in eaach row of a matrix in R?

如何在R的矩阵的eaach行中得到K个最小或最大元素的索引?

E.g. I have matrix:

例如。我有矩阵:

2   3   1  65  2
46  7   9  3   2
9   45  3  5   7
24  65  87 3   6
34  76  54 33  6

I'd like to get Indices matrix of say 2 smallest elements (breaking ties in any way) in each row. the result should be in following format:

我想在每一行中获得指数2个最小元素(以任何方式打破关系)的指数矩阵。结果应采用以下格式:

I tried few commands using sort, apply, arrayInd, which etc. But still unable to get desired result. Any help is welcome.

我尝试使用sort,apply,arrayInd等几个命令,但仍然无法获得所需的结果。欢迎任何帮助。

2 个解决方案

#1

apply(mat, 1, which.max)  #.....largest
apply(mat, 1, which.min)  #.....smallest

t(apply(mat, 1, sort)[ 1:2, ])  # 2 smallest in each row

t(apply(mat, 1, order)[ 1:2, ])  # indices of 2 smallest in each row

Besides using decreasing=TRUE, you could also have used this for the two largest in a row:

除了使用decrease = TRUE之外,您还可以将它用于连续两个最大值:

t(apply(mat, 1, order)[ 5:4, ])

#2

What about

finding the indices of k largest values in each row

找到每行中k个最大值的索引

apply(mat, 1, function(x, k) which(x <= max(sort(x, decreasing = F)[1:k]), arr.ind = T), k)`

finding the indices of k smallest values in each row

找到每行中k个最小值的索引

apply(mat, 1, function(x, k) which(x >= min(sort(x, decreasing = T)[1:k]), arr.ind = T), k)`

On your example, for k <- 2, the former results in

在你的例子中,对于k < - 2,前者导致

     [,1] [,2] [,3] [,4] [,5]
[1,]    2    1    1    2    2
[2,]    4    3    2    3    3

and the latter results in

而后者导致

[[1]]
[1] 1 3 5

[[2]]
[1] 4 5

[[3]]
[1] 3 4

[[4]]
[1] 4 5

[[5]]
[1] 4 5

Change apply's second parameter from 1 to 2 for searching the columns.

将应用的第二个参数从1更改为2以搜索列。

#1

apply(mat, 1, which.max)  #.....largest
apply(mat, 1, which.min)  #.....smallest

t(apply(mat, 1, sort)[ 1:2, ])  # 2 smallest in each row

t(apply(mat, 1, order)[ 1:2, ])  # indices of 2 smallest in each row