查找列号并在一行中计算第二高值 [英] Finding the column number and value the of second highest value in a row

问题描述

I am trying to write some code which identifies the greatest two values for each row and provides their column number and value.

我正在尝试编写一些代码，为每行确定最大的两个值，并提供其列号和值。 > df = data.frame（car = c（2,1,1,1,0），bus = c（0,2,0,1,0），
walk = c（0,3,2 ，0,0），bike = c（0,4,0,0,1））

df = data.frame( car = c (2,1,1,1,0), bus = c (0,2,0,1,0), walk = c (0,3,2,0,0), bike = c(0,4,0,0,1))

我已经设法使用 max 和 max.col 函数来获取最大值。 / p>

I've managed to get it to do this for the maximum value using the max and max.col functions.

df$max = max.col(df,ties.method="first")
df$val = apply(df[ ,1:4], 1, max)

据我所知，相当于第二高价值的功能，所以这样做使事情有点棘手。使用这个代码提供了第二个最高的值，但是（重要的是）不是在有关系的情况下。另外看起来有风险。

As far as I know there are no equivalent functions for the second highest value so doing this has made things a little trickier. Using this code provides the second highest value but (importantly) not in situations with ties. Also it looks risky.

sec.fun <- function (x) {
  max( x[x!=max(x)] )
}

df$val2 <- apply(df[ ,1:4], 1, sec.fun)

理想情况下，解决方案不涉及删除任何原始数据，可用于查找第三，第四...最高价值，但这两个是必需的要求。

Ideally the solution would not involve removing any original data and could be used to find the third, fourth... highest value but neither of these are essential requirements.

推荐答案

尝试这样：

# a function that returns the position of n-th largest
maxn <- function(n) function(x) order(x, decreasing = TRUE)[n]

这是一个关闭，所以你可以这样使用：

this is a closure, so you can use like this:

> # position of the largest
> apply(df, 1, maxn(1))
[1] 1 4 3 1 4
> # position of the 2nd largest
> apply(df, 1, maxn(2))
[1] 2 3 1 2 1
> 
> # value of the largest
> apply(df, 1, function(x)x[maxn(1)(x)])
[1] 2 4 2 1 1
> # value of the 2nd largest
> apply(df, 1, function(x)x[maxn(2)(x)])
[1] 0 3 1 1 0

更新

为什么在这里使用关闭？

Why using closure here?

一个原因是您可以定义一个函数，如：

One reason is that you can define a function such as:

max2 <- maxn(2)
max3 <- maxn(3)

然后使用它

> apply(df, 1, max2)
[1] 2 3 1 2 1
> apply(df, 1, max3)
[1] 3 2 2 3 2

'不知道这个优势是否明显，但我喜欢这样，因为这是更有功能的方式。

I'm not sure if the advantage is obvious, but I like this way, since this is more functional-ish way.

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