[R] reshaping a large dataframe in R

[PIKAL Petr]

Hi

probably not at all simpler

> dat2.p<-split(t(dat), rep(1:(ncol(dat)/4), each=4))
> dat3.p<-as.data.frame(do.call(rbind, lapply(dat2.p, function(x) t(matrix(x, 4,nrow(dat))))))
>
> all.equal(dat3.p, dat3)
[1] TRUE

Cheers
Petr


> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of David L
> Carlson
> Sent: Monday, November 28, 2016 8:27 PM
> To: jean-philippe <jeanphilippe.fontaine at gssi.infn.it>; r-help at r-project.org
> Subject: Re: [R] reshaping a large dataframe in R
>
> There may be a simpler way of getting there, but this works:
>
> > rows <- 500
> > cols <- 4004
> > dat <- as.data.frame(t(replicate(rows, 1:cols))) dat[c(1:3, 500),
> > c(1:4, 4001:4004)]
>     V1 V2 V3 V4 V4001 V4002 V4003 V4004
> 1    1  2  3  4  4001  4002  4003  4004
> 2    1  2  3  4  4001  4002  4003  4004
> 3    1  2  3  4  4001  4002  4003  4004
> 500  1  2  3  4  4001  4002  4003  4004
> > dat2 <- array(as.matrix(dat), dim=c(rows, 4, cols/4))
> > dat3 <- as.data.frame(matrix(aperm(dat2, c(1, 3, 2)), rows*cols/4, 4))
> > head(dat3)
>   V1 V2 V3 V4
> 1  1  2  3  4
> 2  1  2  3  4
> 3  1  2  3  4
> 4  1  2  3  4
> 5  1  2  3  4
> 6  1  2  3  4
> > tail(dat3)
>          V1   V2   V3   V4
> 500495 4001 4002 4003 4004
> 500496 4001 4002 4003 4004
> 500497 4001 4002 4003 4004
> 500498 4001 4002 4003 4004
> 500499 4001 4002 4003 4004
> 500500 4001 4002 4003 4004
>
> -------------------------------------
> David L Carlson
> Department of Anthropology
> Texas A&M University
> College Station, TX 77840-4352
>
> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of jean-
> philippe
> Sent: Monday, November 28, 2016 3:07 AM
> To: r-help at r-project.org
> Subject: [R] reshaping a large dataframe in R
>
> dear all,
>
> I have a dataframe of 500 rows and 4004 columns that I would like to reshape
> to a dataframe of 500500 rows and 4 columns. That is from this
> dataframe:
>
> V1 V2 V3 V4 ... V4001 V4002 V4003 V4004
>
> 1 2 3 4 ... 4001 4002 4003 4004
>
> 1 2 3 4 ... 4001 4002 4003 4004
>
> 1 2 3 4 ... 4001 4002 4003 4004
>
> ... ... ... ... ... ... ... ... ... ... ... ... ...
>
> 1 2 3 4 ... 4001 4002 4003 4004
>
> I would like :
>
>
> V1 V2 V3 V4
>
> 1 2 3 4
>
> 1 2 3 4
>
> 1 2 3 4
>
> 1 2 3 4
>
> ... ... ... ... ... ... ... ... ...
>
> 4001 4002 4003 4004
>
> 4001 4002 4003 4004
>
> 4001 4002 4003 4004
>
> ... ... ... ... ...
>
> 4001 4002 4003 4004
>
> I tried already to use y=matrix(as.matrix(dataGaus[[1]]),500500,4)
> (where dataGaus is my dataframe) but it doesn't give the expected result. I
> tried also to use reshape but I can't manage to use it to reproduce the result
> (and I have been through lot of posts on StackOverflow and on the net). In
> python, we can do this with a simple command
> numpy.array(dataGaus[[1]]).reshape(-1,4). For some reasons, I am doing my
> analysis in R, and I would like to know if there is a function which does the
> same thing as the reshape(-1,4) of numpy in Python?
>
> Thanks in advance, best
>
>
> Jean-Philippe
>
> --
> Jean-Philippe Fontaine
> PhD Student in Astroparticle Physics,
> Gran Sasso Science Institute (GSSI),
> Viale Francesco Crispi 7,
> 67100 L'Aquila, Italy
> Mobile: +393487128593, +33615653774
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> and provide commented, minimal, self-contained, reproducible code.

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