[R] reshape data, adding rows to dataframe

[Petr Savicky]

On Wed, Feb 02, 2011 at 01:13:11AM -0800, Lucia Rueda wrote:
> 
> Hello everyone,
> 
> I have a data set like this:
> 
> > head( fish_transect)
>   ID_TRANSECT ID_PROJECT   DE_ZONE DE_LOCALITY DE_SECTOR MES
> 1          42         MB Tarragona    Creixell Control I   9
> 2          42         MB Tarragona    Creixell Control I   9
> 3          42         MB Tarragona    Creixell Control I   9
> 4          42         MB Tarragona    Creixell Control I   9
> 5          42         MB Tarragona    Creixell Control I   9
> 6          42         MB Tarragona    Creixell Control I   9
>                ID_SPECIES         WEIGHT  SIZE   N    FAMILIA
> 1 Spondyliosoma cantharus    15.64     10     1    Sparidae
> 2  Symphodus melanocercus  11.21     10      1   Labridae
> 3       Diplodus vulgaris         30.20     10      2   Sparidae
> 4       Diplodus vulgaris         52.24     12      2   Sparidae
> 5         Diplodus sargus        221.41    14     5    Sparidae
> 6      Diplodus annularis         3.47       6      1    Sparidae
> 
> I have been trying to duplicate the rows where N> 1, that is I want a row
> for each animal. Right now as you can see I have for example 5 D. sargus
> which are 14 cm length and so on. How can I get 1 row for each animal? I've
> been trying the reshape function without success. I also tried in access but
> couldn't do it either.

Hello.

Let me use a simpler example for testing.

  dat <- data.frame(animal=c("a", "b", "c"), N=c(2, 1, 3))
  dat

    animal N
  1      a 2
  2      b 1
  3      c 3

Is the following operation what you want in terms of this small example?

  expand <- dat[rep(1:nrow(dat), times=dat$N), ]
  rownames(expand) <- NULL
  expand

    animal N
  1      a 2
  2      a 2
  3      b 1
  4      c 3
  5      c 3
  6      c 3

Hope this helps.

Petr Savicky.