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

问题描述

我试图了解order()函数的工作方式.我的印象是它返回了索引的排列，排序后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

我希望它返回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.

有人可以帮助我了解此函数的返回值吗?

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

推荐答案

This seems to explain it.

order的定义是a[order(a)]在 顺序增加.这适用于您的示例，其中正确的 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，它会返回 元素
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
所以rank告诉您数字的顺序， 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，但是尝试plot(a, rank(a)/length(a),type="S") 这很混乱，因为数据的顺序不是递增的

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

如果您做了
oo<-order(a)
plot(a[oo],rank(a[oo])/length(a),type="S")
或简单地
oo<-order(a)
plot(a[oo],(1:length(a))/length(a)),type="S")
您会得到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，您正在考虑排名.

I'll bet you're thinking of rank.

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