理解 order() 函数 [英] Understanding the order() function

问题描述

我正在尝试了解 order() 函数的工作原理.我的印象是它返回了一个索引排列，当排序时，会对原始向量进行排序.

I'm trying to understand how the order() function works. I was under the impression that it returned a permutation of indices, which when sorted, would sort the original vector.

例如

> a <- c(45,50,10,96)
> order(a)
[1] 3 1 2 4

我原以为这会返回 c(2, 3, 1, 4)，因为排序的列表将是 10 45 50 96.

I would have expected this to return c(2, 3, 1, 4), since the list sorted would be 10 45 50 96.

谁能帮我理解这个函数的返回值?

Can someone help me understand the return value of this function?

推荐答案

这似乎可以解释它.

order 的定义是 a[order(a)] 在递增顺序.这适用于您的示例，其中正确顺序是第四个，第二个，第一个，然后是第三个元素.

The definition of order is that a[order(a)] is in increasing order. This works with your example, where the correct order is the fourth, second, first, then third element.

您可能一直在寻找 rank，它返回元素
<代码>R>a <- c(4.1, 3.2, 6.1, 3.1)
<代码>R>订单(一)
[1] 4 2 1 3
<代码>R>排名(a)
[1] 3 2 4 1
所以 rank 告诉你数字的顺序，order 告诉您如何按升序获取它们.

You may have been looking for rank, which returns the rank of the elements
R> a <- c(4.1, 3.2, 6.1, 3.1)
R> order(a)
[1] 4 2 1 3
R> rank(a)
[1] 3 2 4 1
so rank tells you what order the numbers are in, order tells you how to get them in ascending order.

plot(a, rank(a)/length(a)) 将给出 CDF 的图形.看看为什么order 很有用，不过，试试 plot(a, rank(a)/length(a),type="S")这让人一团糟，因为数据不是按升序排列的

plot(a, rank(a)/length(a)) will give a graph of the CDF. To see why order is useful, though, try plot(a, rank(a)/length(a),type="S") which gives a mess, because the data are not in increasing order

如果你这样做了
oo<-order(a)
plot(a[oo],rank(a[oo])/length(a),type="S")
或者干脆
oo<-order(a)
plot(a[oo],(1:length(a))/length(a)),type="S")
您将获得 CDF 的折线图.

If you did
oo<-order(a)
plot(a[oo],rank(a[oo])/length(a),type="S")
or simply
oo<-order(a)
plot(a[oo],(1:length(a))/length(a)),type="S")
you get a line graph of the CDF.

我敢打赌你在考虑排名.

I'll bet you're thinking of rank.

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