如何在data.table中进行负/ nomatch /反向搜索？ [英] How do I do a negative / nomatch / inverse search in data.table?

问题描述

如果我想选择data.table中的所有行，在关键变量中不包含特定值使用二叉搜索会发生什么？顺便问一下，我想做什么是正确的行话？是nojoin吗？是否为否定选择？

  DT = data.table（x = rep（c（a，b ，c），每个= 3），y = c（1,3,6），v = 1：9）
 setkey（DT，x）
  / pre> 
 
 
允许对所有x ==a行使用二进制搜索进行肯定选择
  DT [a] 
  
相反。我想要所有不是a的行，其中x！=a
  DT [x！= a] 
  
这是一个矢量扫描。上面的行工作，但使用矢量扫描。我想使用二进制。我期待下面的工作，但唉... 
  DT [！a] 
 DT [ - a] 
  
上面两个不工作，试图和nomatch一起玩， 
解决方案
这个习语是这样的：
  DT [-DT [a，which = TRUE]] 
 
xyv 
 1：b 1 4 
 2：b 3 5 
 3： b 6 6 
 4：c 1 7 
 5：c 3 8 
 6：c 6 9 
  
 
 
 
 
 
 
灵感来源：
 
 
 
 
 
邮寄名单张贴< a href =http://lists.r-forge.r-project.org/pipermail/datatable-help/2010-July/000140.html =noreferrer>返回选择/加入不匹配？ 
 
 
上一个问题不与data.tables非联接 
 
 
 Matthew Dowle的 answer 到将R的数据框移植到数据表：如何识别重复的行？ 
 
 
 
 
 
 
 
 
 更新。 v1.8.3中的新增内容是非连接语法。 Farrel的第一个期望（！而不是  -  ）已经实现：
  DT [-DT [a，which = TRUE，nomatch = 0]，...]＃old idiom 
 DT [！ ..]＃相同的结果，现在首选。 
  
请参阅 NEWS  item for more detailed information and example。
 
What happens if I want to select all the rows in a data.table that do not contain a particular value in the key variable using binary search? By the way, what is the correct jargon for what I want to do? Is it "nojoin"? Is it "negative selection"?
DT = data.table(x=rep(c("a","b","c"),each=3), y=c(1,3,6), v=1:9)
setkey(DT,x)
Lets do a positive selection for all rows where x=="a" but using binary search
DT["a"]
That's beautiful but I want the opposite of that. I want all the rows that are not "a" in other words where x!="a"
DT[x!="a"]
That is a vector scanning. The above line works but is uses vector scanning. I want to use binary. I was expecting the following to work, but alas...
DT[!"a"]
DT[-"a"]
The above two do not work and trying to play with nomatch got me nowhere.
解决方案
The idiom is this:
DT[-DT["a", which=TRUE]]

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




Inspiration from:


The mailing list posting Return Select/Join that does NOT match?
The previous question non-joins with data.tables
Matthew Dowle's answer to Porting set operations from R's data frames to data tables: How to identify duplicated rows?




Update. New in v1.8.3 is not-join syntax. Farrel's first expectation (! rather than -) has been implemented :
DT[-DT["a",which=TRUE,nomatch=0],...]   # old idiom
DT[!"a",...]                            # same result, now preferred.
See the NEWS item for more detailed info and example.

                        
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