如何避免在数据表中进行向量搜索

问题描述

我有一个data.table X，我想创建一个基于2个字符变量的变量

  X [ varC：=（（VarA ==A&！is.na（VarA））
 |（VarA ==AB& VarB ==B&！is.na &！is.na（VarB））
）
] 
  

代码工作，但它是非常慢，因为它做矢量扫描2个字符变量。注意，我没有通过VarA和VarB设置键claim4表。在data.table中有一个正确的方法来做到这一点？

更新1：我不使用setkey这个转换，因为我已经使用setkey年，ID）用于其他变量转换。

更新2：我用Matthew的方法对我的方法进行了基准测试，他的速度更快了：

 测试复制已过相对user.self sys.self user.child sys.child 
 2 Matthew 100 3.377 1.000 2.596 0.605 0 0 
 1 vectorSearch 100 200.437 59.354 76.628 40.260 0 0 
  

是setkey，然后re-setkey再次有点冗长：）

解决方案

如何：

  setkey（X，VarA，VarB）
 X [，varC：= FALSE] 
 X [A，varC：= TRUE] 
 X [J（A，AB），varC：= TRUE] 
  

或者在一行中（保存变量 X 的重复并演示）：

  X [，varC：= FALSE] [A，varC：= TRUE] [J（A，AB），varC：= TRUE] 
  
 
 
 
为了避免按照要求设置密钥，如何操作手动辅助密钥：
  S = setkey（X [，list（VarA，VarB，i = seq_len（.N））]，VarA，VarB）
 X [ varC：= FALSE] 
 X [S [A，i] [[2]]，varC：= TRUE] 
 X [ ] [[3]]，varC：= TRUE] 
  
现在很清楚，因此，是将其构建到语法中;例如
  set2key（X，varA，varB）
 X [...某种方式指定哪个键join to ...，varC：= TRUE] 
  
在此期间，如上所示。
 
I have a data.table X that I would like to create a variable based on 2 character variables
   X[, varC :=((VarA =="A" & !is.na(VarA))
               | (VarA == "AB" & VarB =="B" & !is.na(VarA) & !is.na(VarB))
                )
      ]
This code works but it is very slow, because it does vector scan on 2 char variables. Note that I don't setkey claims4 table by VarA and VarB. Is there a "right" way to do this in data.table?
Update 1:  I don't use setkey for this transformation because I already use setkey(X, Year, ID) for other variable transformations.  If I do, I need to reset keys back to Year, ID after this transformation.
Update 2: I did benchmark my approach with Matthew's approach, and his is much faster:
          test replications elapsed relative user.self sys.self user.child sys.child
2 Matthew               100   3.377    1.000     2.596    0.605          0         0
1 vectorSearch          100 200.437   59.354    76.628   40.260          0         0
The only minor thing is setkey then re-setkey again is somewhat verbose :)
 解决方案 
How about :
setkey(X,VarA,VarB)
X[,varC:=FALSE]
X["A",varC:=TRUE]
X[J("A","AB"),varC:=TRUE]
or, in one line (to save repetitions of the variable X and to demonstrate) :
X[,varC:=FALSE]["A",varC:=TRUE][J("A","AB"),varC:=TRUE]
To avoid setting the key, as requested, how about a manual secondary key :
S = setkey(X[,list(VarA,VarB,i=seq_len(.N))],VarA,VarB)
X[,varC:=FALSE]
X[S["A",i][[2]],varC:=TRUE]
X[S[J("A","AB"),i][[3]],varC:=TRUE]
Now clearly, that syntax is ugly. So FR#1007 Build in secondary keys is to build that into the syntax; e.g.,
set2key(X,varA,varB)
X[...some way to specify which key to join to..., varC:=TRUE]
In the meantime it's possible, just manually, as shown above.
                        
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