Re: [R] reshaping some data

Sundar Dorai-Raj Tue, 14 Sep 2004 10:25:54 -0700

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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] 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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Re: [R] reshaping some data

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