dataframe - R self reference

Question

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

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

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 

?

question from:https://stackoverflow.com/questions/7768686/r-self-reference

Answer 1

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

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

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.

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