R自我参考 [英] R self reference

问题描述

在RI发现自己在做这样的事情很多：

In R I find myself doing something like this a lot:

adataframe [adataframe $ col == something ]< - dataframe [adataframe $ col == something]] + 1

漫长而乏味有一些方法我

引用我正在改变的对象，如

This way is kind of long and tedious. Is there some way for me
to reference the object I am trying to change such as

adataframe[adataframe$col==something]<-$self+1 

？

推荐答案

尝试打包数据.table 及其：= 运算符。它非常快，很短。

Try package data.table and its := operator. It's very fast and very short.

DT[col1==something, col2:=col3+1]

第一部分 col1 == something 是该子集。你可以把任何东西放在这里，并使用列名，就像它们是变量一样;即不需要使用 $ 。然后第二部分 col2：= col3 + 1 将RHS分配给该子集内的LHS，其中可以将列名分配为如同变量​​一样。 ：= 通过引用分配。没有任何对象的副本被采取，所以比 < - $ / code>， = ，在和转换。

The first part col1==something is the subset. You can put anything here and use the column names as if they are variables; i.e., no need to use $. Then the second part col2:=col3+1 assigns the RHS to the LHS within that subset, where the column names can be assigned to as if they are variables. := is assignment by reference. No copies of any object are taken, so is faster than <-, =, within and transform.

此外，即将在v1.8.1中实现， j 的语法的最终目标是允许 j ：= c>像这样将它与相结合，请参阅问题：何时应该在data.table中使用：= 运算符。

Also, soon to be implemented in v1.8.1, one end goal of j's syntax allowing := in j like that is combining it with by, see question: when should I use the := operator in data.table.

UDPDATE：在2012年7月，确实发布了（：= 。

UDPDATE : That was indeed released (:= by group) in July 2012.

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