string 在字符串键 `order(-x,v)` 上按降序对 data.table 中的行进行排序会在 data.table 1.9.4 或更早版本上出现错误
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Sort rows in data.table in decreasing order on string key `order(-x,v)` gives error on data.table 1.9.4 or earlier
提问by nhern121
Let's say I have the following data.tablein R:
比方说，我有以下data.table的R：
library(data.table)
DT = data.table(x=rep(c("b","a","c"),each=3), y=c(1,3,6), v=1:9)
I want to order it by two columns (say columns xand v). I used this:
我想按两列（比如列x和v）排序。我用过这个：
DT[order(x,v)] # sorts first by x then by v (both in ascending order)
But now, I want to sort it by x(in decreasing order) and have the following code:
但是现在，我想按x（按降序）对其进行排序并具有以下代码：
DT[order(-x)] #Error in -x : invalid argument to unary operator
Therefore, I think this error is due to the fact that class(DT$x)=character. Could you give me any suggestion in order to solve this issue?
因此，我认为这个错误是由于class(DT$x)=character. 你能给我任何建议来解决这个问题吗？
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.
我知道我可以使用DT[order(x,decreasing=TRUE)]，但我想知道同时使用两种方式（有些减少，有些增加）按几列排序的语法。
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?
注意，如果使用DT[order(-y,v)]结果没问题，但如果使用DT[order(-x,v)]则出现错误。所以，我的问题是：如何解决这个错误？
回答by Matthew Plourde
Update
更新
data.tablev1.9.6+ now supports OP's original attempt and the following answer is no longer necessary.
data.tablev1.9.6+ 现在支持 OP 的原始尝试，不再需要以下答案。
You can use DT[order(-rank(x), y)].
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
回答by James
You can only use -on the numeric entries, so you can use decreasing and negate the ones you want in increasing order:
您只能-在数字条目上使用，因此您可以按递增顺序使用递减和否定您想要的条目：
DT[order(x,-v,decreasing=TRUE),]
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
回答by Pankil Shah
DT[order(-x)]works as expected. I have data.table version 1.9.4. Maybe this was fixed in a recent version.
Also, I suggest the setorder(DT, -x)syntax in keeping with the set*commands like setnames, setkey
DT[order(-x)]按预期工作。我有 data.table 版本 1.9.4。也许这是在最近的版本中修复的。
另外，我建议setorder(DT, -x)使用符合set*命令的语法，例如setnames，setkey
