[R] foreloop? aggregating time series data into groups

[David Winsemius]

On Nov 1, 2010, at 3:34 PM, blurg wrote:

>
> I have a data set similar to the set below where 1 and 2 indicate test
> results and 0 indicates time points in between where there are no test
> results.  I would like to allocate the time points leading up to a  
> test
> result with the value of the test result.
>
> What I have:     What I want:
> 1                     1
> 0                     1
> 0                     1
> 0                     1
> 1                     1
> 0                     2
> 0                     2
> 2                     2
> 0                     1
> 0                     1
> 1                     1
> 0                     2
> 2                     2
>
> I have attempted methods creating a data.frame of the the breaks/ 
> changes in
> of values to from 0 to 1 or to 2.
> x<-c(0,2,0,1,0,0,0,0,1,0,1,0,0,0,2,1,0,0,0,2,0,0,0,1)
> x1 <- which(diff(x) == 1)
> x2 <- which(diff(x) == 2)

Not sure how long you longest run of zeros is but repeate applications  
of htis method n-such times will fill in in the backward direction:

 > xna <- x
 > xna[xna==0] <- NA
 > xna[which(is.na(xna))] <- xna[which(is.na(xna))+1]
 > xna
  [1]  2  2  1  1 NA NA NA  1  1  1  1 NA NA  2  2  1 NA NA  2  2 NA  
NA  1  1
 > xna[which(is.na(xna))] <- xna[which(is.na(xna))+1]
 > xna
  [1]  2  2  1  1 NA NA  1  1  1  1  1 NA  2  2  2  1 NA  2  2  2 NA   
1  1  1
 > xna[which(is.na(xna))] <- xna[which(is.na(xna))+1]
 > xna[which(is.na(xna))] <- xna[which(is.na(xna))+1]
 > xna[which(is.na(xna))] <- xna[which(is.na(xna))+1]
 > xna
  [1] 2 2 1 1 1 1 1 1 1 1 1 2 2 2 2 1 2 2 2 2 1 1 1 1

I'm not sure that conversion to NA is needed. The indexing with  
which(x==0) and which(x==0+1 might work as well. Yep... that work's too:

 > x
  [1] 0 2 0 1 0 0 0 0 1 0 1 0 0 0 2 1 0 0 0 2 0 0 0 1
 > x[which(x==0)] <- x[which(x==0)+1]
 > x
  [1] 2 2 1 1 0 0 0 1 1 1 1 0 0 2 2 1 0 0 2 2 0 0 1 1
 > x[which(x==0)] <- x[which(x==0)+1]
 > x[which(x==0)] <- x[which(x==0)+1]
 > x[which(x==0)] <- x[which(x==0)+1]
 > x
  [1] 2 2 1 1 1 1 1 1 1 1 1 2 2 2 2 1 2 2 2 2 1 1 1 1


-- 
David


>
> What ever the solution, I can't be entered by hand due to the size  
> of the
> dataset (>10 million and change). Any ideas?  This is my first time  
> posting
> to this forum and I am relatively new to R, so please don't flame me  
> to
> hard.  Desperate times call for desperate measures.  Thanks.
> -- 


David Winsemius, MD
West Hartford, CT