[R] Quicker way of combining vectors into a data.frame

[Prof Brian Ripley]

If you are prepared to give up most of the sanity checks, see this at the 
bottom of read.table:

     ##	this is extremely underhanded
     ##	we should use the constructor function ...
     ##	don't try this at home kids

     class(data) <- "data.frame"
     row.names(data) <- row.names
     data

So create a (named?) list with your vectors in it, assign class 
"data.frame" and then row.names(data) <- NULL

On Thu, 30 Nov 2006, Gavin Simpson wrote:

> Hi,
>
> In a function, I compute 10 (un-named) vectors of reasonable length
> (4471 in the particular example I have to hand) that I want to combine
> into a data frame object, that the function will return.
>
> This is very slow, so *I'm* doing something wrong if I want it to be
> quick and efficient, though I'm not sure what the best way to do this
> would be.
>
> I know it is the combining into data frame bit that is slow, because
> I've Rprof'ed it:
>
> $by.self
>                        self.time self.pct total.time total.pct
> "names<-.default"           16.58     52.8      16.58      52.8
> "unlist"                     7.22     23.0       7.26      23.1
> "data.frame"                 1.72      5.5      29.38      93.6
> "duplicated.default"         1.66      5.3       1.66       5.3
> "+"                          1.20      3.8       1.20       3.8
> "list"                       0.40      1.3       0.40       1.3
> "as.data.frame.numeric"      0.28      0.9       3.32      10.6
> "apply"                      0.26      0.8       1.70       5.4
> "pmatch"                     0.22      0.7       0.22       0.7
> "paste"                      0.20      0.6       0.90       2.9
> "deparse"                    0.14      0.4       0.70       2.2
> "eval"                       0.12      0.4      31.28      99.7
> "names<-"                    0.12      0.4      16.70      53.2
> "FUN"                        0.12      0.4       1.32       4.2
> "names"                      0.12      0.4       0.14       0.4
> "as.list.default"            0.12      0.4       0.12       0.4
> "duplicated"                 0.10      0.3       1.76       5.6
> "gc"                         0.10      0.3       0.10       0.3
>
> And I stepped through it under debug() and all the calculations before
> are quick, and then this bit takes a little over 20 seconds to complete
>
> fab <- data.frame(lc.ratio = lc.ratio, Q = Q,
>                     fNupt = fNupt,
>                     rho.n = rho.n, rho.s = rho.s,
>                     net.Nimm = net.Nimm,
>                     net.Nden = net.Nden,
>                     CLminN = CLminN,
>                     CLmaxN = CLmaxN,
>                     CLmaxS = CLmaxS)
>
> I can get it down to c. 5 seconds if I do (not Rprof'ed):
>
> fab <- data.frame(lc.ratio, Q,
>                     fNupt,
>                     rho.n, rho.s,
>                     net.Nimm,
>                     net.Nden,
>                     CLminN,
>                     CLmaxN,
>                     CLmaxS)
>
> But this still seems quite a long time, so I'm thinking that there must
> be a quicker of doing what I want (end up with a data.frame with the 10
> vectors in it).
>
> Can anyone enlighten me?
>
>> version
>               _
> platform       i686-pc-linux-gnu
> arch           i686
> os             linux-gnu
> system         i686, linux-gnu
> status         Patched
> major          2
> minor          4.0
> year           2006
> month          10
> day            03
> svn rev        39576
> language       R
> version.string R version 2.4.0 Patched (2006-10-03 r39576)
>
>> sessionInfo()
> R version 2.4.0 Patched (2006-10-03 r39576)
> i686-pc-linux-gnu
>
> locale:
> LC_CTYPE=en_GB.UTF-8;LC_NUMERIC=C;LC_TIME=en_GB.UTF-8;LC_COLLATE=en_GB.UTF-8;LC_MONETARY=en_GB.UTF-8;LC_MESSAGES=en_GB.UTF-8;LC_PAPER=en_GB.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_GB.UTF-8;LC_IDENTIFICATION=C
>
> attached base packages:
> [1] "methods"   "stats"     "graphics"  "grDevices" "utils"
> "datasets"
> [7] "base"
>
> Thanks in advance,
>
> G
>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595