[R] reshaping some data

[Berton Gunter]

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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