[R] reshaping some data
Sundar Dorai-Raj
sundar.dorai-raj at PDF.COM
Tue Sep 14 19:13:48 CEST 2004
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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>>
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