[R] Adding Column to Data Frames Using a Loop

[arun]

Hi,
You could use:
library(plyr)
for(i in letters[24:26]) assign(i,mutate(get(i),V4=V2+V3))
 x
 # V1 V2 V3 V4
#1  1  2  3  5
#2  1  2  3  5
#3  1  2  2  4
#4  1  2  2  4
#5  1  1  1  2
 y
#  V1 V2 V3 V4
#1  1  2  3  5
#2  1  2  3  5
#3  1  2  2  4
#4  1  2  2  4
#5  1  1  1  2


A.K.


>Dear R Helpers, 
>
>I am trying to do calculations on multiple data frames and do not want to 
>create a list of them to go through each one.  I know that lists have many 
>wonderful advantages, but I believe the better thing is to work df by df 
>for my particular situation.  For background, I have already received some 
>wonderful help on how to handle some situations, such as removing columns: 
>
>
>x=as.data.frame(matrix(c(1,2,3, 
 >       1,2,3, 
  >      1,2,2, 
   >     1,2,2, 
   >    1,1,1),ncol=3,byrow=T)) 
>
>y=as.data.frame(matrix(c(1,2,3, 
 >       1,2,3, 
  >      1,2,2, 
  >      1,2,2, 
  >     1,1,1),ncol=3,byrow=T)) 
>
 >z=as.data.frame(matrix(c(1,2,3, 
 >       1,2,3, 
  >      1,2,2, 
  >      1,2,2, 
  >     1,1,1),ncol=3,byrow=T)) 
>
>for(i in letters[24:26] ) assign( i, subset(get(i), select=-c(V1))  ) 
>x 
>y 
>z 
>
>And I figured how to do further processing using functions: 
>
>myfunc<-function(DF){ 
> DF$V4<-DF$V2+DF$V3 
 >return(DF) 
>} 
>for(i in letters[24:26] ) assign( i, myfunc(get(i))) 
>
>But if I want to do a rather simple calculation and store it as a new 
>column in each data frame such as 
>
>x$V4<-x$V2+x$V3 
>y$V4<-y$V2+y$V3 
>z$V4<-z$V2+z$V3 
>
>is there a simpler way to do this than building a function as shown above? 
 >I tried a few variations of 
>
>i<-24 
>assign(paste(i,"$V4",sep=""),paste(get(i),"$V2+",get(i),"$V3",sep="")) 
>
>but keep getting syntax errors. 
>
>If anyone could help with the syntax as to how to accomplish the 
>calculation above without building a function, I would really appreciate 
>it. 
>
>--John Sparks