在data.table(R)中排序行 [英] Sort rows in data.table (R)
问题描述
假设我在 R
中有以下 data.table
:
library(data.table)
DT = data.table(x=rep(c("b","a","c"),each=3), y=c(1,3,6), v=1:9)
我想通过两列来排序(例如 x
和 v
)。我使用这个:
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)
但现在,我想通过 x
(以递减顺序),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,我认为这个错误是由于 class(DT $ x)= character
。
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,decrease = TRUE)]
,但我想知道使用两种方法(一些减少,一些增加)同时对多列进行排序的语法。
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,如果您使用 DT [order(-y,v)]
,结果是确定,你使用 DT [order(-x,v)]
有一个错误。因此,我的问题是:如何解决此错误?
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 现在支持OP的原始尝试,并且不再需要以下答案。
Update
data.table 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
这篇关于在data.table(R)中排序行的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!