[R] Vectorizing a loop

[Petr Savicky]

On Tue, Feb 07, 2012 at 11:39:42AM -0500, Alexander Shenkin wrote:
> Hello Folks,
> 
> I'm trying to vectorize a loop that processes rows of a dataframe.  It
> involves lots of conditionals, such as "If column 10 == 3, and if column
> 3 is True, and both column 5 and 6 are False, then set column 4 to True".
> 
> So, for example, any ideas about vectorizing the following?
> 
> df = data.frame( list(a=c(1,2,3,4), b=c("a","b","c","d"), c=c(T,F,T,F),
> d=NA, e=c(F,F,T,T)) )
> 
> for (i in 1:nrow(df)) {
> 
>     if (df[i,3] %in% c(FALSE,NA) & (df[i,1] > 2 | df[i,5]) ) {
>         df[i,4] = 1
>     }
> 
>     if (df[i,5] %in% c(TRUE, NA) & df[i,2] == "b") {
>         df[i,4] = 2
>         df[i,5] = T
>     }
> 
> }

Hi.

Try the following.

  cond1 <- (df[,3] %in% c(FALSE,NA)) & (df[,1] > 2 | df[,5])
  df[,4] <- ifelse(cond1, 1, df[,4])
  cond2 <- (df[,5] %in% c(TRUE, NA)) & (df[,2] == "b")
  df[,4] <- ifelse(cond2, 2, df[,4])
  df[,5] <- ifelse(cond2, TRUE, df[,5])

Hope this helps.

Petr Savicky.