在字符串键`order(-x，v)`上以降序对data.table中的行进行排序会在data.table 1.9.4或更早版本上给出错误 [英] Sort rows in data.table in decreasing order on string key `order(-x,v)` gives error on data.table 1.9.4 or earlier

问题描述

假设我在R中具有以下data.table:

  library(data.table)
  DT = data.table(x=rep(c("b","a","c"),each=3), y=c(1,3,6), v=1:9)

我想按两列对其进行排序(例如，列x和v).我用了这个:

I want to order it by two columns (say columns x and v). I used this:

 DT[order(x,v)] # sorts first by x then by v (both in ascending order)

但是现在，我想按x对其进行排序(以降序排列)，并具有以下代码:

But now, I want to sort it by x (in decreasing order) and have the following code:

  DT[order(-x)] #Error in -x : invalid argument to unary operator

因此，我认为此错误是由于class(DT$x)=character这一事实造成的.为了解决这个问题，您能给我什么建议吗?

Therefore, I think this error is due to the fact that class(DT$x)=character. Could you give me any suggestion in order to solve this issue?

我知道我可以使用DT[order(x,decreasing=TRUE)]，但是我想知道语法同时使用两种方式(有些减少，有些增加)按几列排序.

I know I can use DT[order(x,decreasing=TRUE)], but I want to know the syntax to sort by several columns using both ways (some decreasing, some increasing) at the same time.

请注意，如果使用DT[order(-y,v)]，则结果正常，但如果使用DT[order(-x,v)]，则会出现错误.所以，我的问题是:如何解决这个错误?

Note that if you use DT[order(-y,v)] the result is ok, but if you use DT[order(-x,v)] there is an error. So, my question is: how to solve this error?

推荐答案

更新

data.table v1.9.6 +现在支持OP的原始尝试，不再需要以下答案.

Update

data.table v1.9.6+ now supports OP's original attempt and the following answer is no longer necessary.

您可以使用DT[order(-rank(x), y)].

   x y v
1: c 1 7
2: c 3 8
3: c 6 9
4: b 1 1
5: b 3 2
6: b 6 3
7: a 1 4
8: a 3 5
9: a 6 6

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