[R] reshaping some data

[Sundar Dorai-Raj]

Bert,
   Coming up with "nvec" was what I was missing. Modifying your solution 
slightly, here's what I ended up with:

z <- x[, nmx]
nvec <- seq(length(nmx))
z <- unlist(z[, rep(nvec, repy)])
z2 <- data.frame(x = z, y = y, row.names = NULL)

Thanks again,

--sundar

Berton Gunter wrote:

> Sundar:
> 
> As I understand it, you can easily create an index variable (a pointer,
> actually) that will pick out the y columns in order:
> 
> z<-yourdataframe
> y<-as.vector(z[,indexvar])
> 
> So if you could cbind() the x's, you'd be all set.
> 
> Again, assuming I understand correctly, the x column you want is:
> 
> x<-z[,-indexvar] ## still a frame/matrix
> nvec<-seq(length=ncol(x))
> x<-as.vector(x[,rep(nvec,times=nvec)])
> 
> HTH -- and even if I got it wrong, it was fun, so thanks.
> 
> -- Bert
> 
> -- Bert Gunter
> Genentech Non-Clinical Statistics
> South San Francisco, CA
>  
> "The business of the statistician is to catalyze the scientific learning
> process."  - George E. P. Box
>  
>  
> 
> 
>>-----Original Message-----
>>From: r-help-bounces at stat.math.ethz.ch 
>>[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Sundar 
>>Dorai-Raj
>>Sent: Tuesday, September 14, 2004 9:16 AM
>>To: R-help
>>Subject: [R] reshaping some data
>>
>>Hi all,
>>   I have a data.frame with the following colnames pattern:
>>
>>x1 y11 x2 y21 y22 y23 x3 y31 y32 ...
>>
>>I.e. I have an x followed by a few y's. What I would like to 
>>do is turn 
>>this wide format into a tall format with two columns: "x", "y". The 
>>structure is that xi needs to be associated with yij (e.g. x1 should 
>>next to y11 and y12, x2 should be next to y21, y22, and y23, etc.).
>>
>>  x   y
>>x1 y11
>>x2 y21
>>x2 y22
>>x2 y23
>>x3 y31
>>x3 y32
>>...
>>
>>I have looked at ?reshape but I didn't see how it could work 
>>with this 
>>structure. I have a solution using nested for loops (see below), but 
>>it's slow and not very efficient. I would like to find a vectorised 
>>solution that would achieve the same thing.
>>
>>Now, for an example:
>>
>>x <- data.frame(x1 =  1: 5, y11 =  1: 5,
>>                 x2 =  6:10, y21 =  6:10, y22 = 11:15,
>>                 x3 = 11:15, y31 = 16:20,
>>                 x4 = 16:20, y41 = 21:25, y42 = 26:30, y43 = 31:35)
>># which are the x columns
>>nmx <- grep("^x", names(x))
>># which are the y columns
>>nmy <- grep("^y", names(x))
>># grab y values
>>y <- unlist(x[nmy])
>># reserve some space for the x's
>>z <- vector("numeric", length(y))
>># a loop counter
>>k <- 0
>>n <- nrow(x)
>>seq.n <- seq(n)
>># determine how many times to repeat the x's
>>repy <- diff(c(nmx, length(names(x)) + 1)) - 1
>>for(i in seq(along = nmx)) {
>>   for(j in seq(repy[i])) {
>>     # store the x values in the appropriate z indices
>>     z[seq.n + k * n] <- x[, nmx[i]]
>>     # move to next block in z
>>     k <- k + 1
>>   }
>>}
>>data.frame(x = z, y = y, row.names = NULL)
>>
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