R help - Nov 2009 - person-level to person-period xfm

Dear R experts,

I have a so-called person-level data frame that I need to transform
into a person-period data frame.

If the lingo is unclear, the data have one row for each subject, with
repeated measures data each in a separate column.

I need to transform these data so that each subject has multiple rows,
one for each repeated measure value.

Is there a quick-and-dirty way to do this transformation?

Many thanks,

-- 
Robert Terwilliger
Biomedical Physicist
Laboratory of Neurocognitive Development
Western Psychiatric Institute and Clinic
University of Pittsburgh Medical Center
Loeffler Building
121 Meyran Avenue  #114
Pittsburgh, PA 15213
412.383.8174  - Office
412.383.8179 - Fax
em: raterwil at gmail.com
http://www.wpic.pitt.edu/research/lncd/

Robert Terwilliger wrote:
> Dear R experts,
>
> I have a so-called person-level data frame that I need to transform
> into a person-period data frame.
>
> If the lingo is unclear, the data have one row for each subject, with
> repeated measures data each in a separate column.
>
> I need to transform these data so that each subject has multiple rows,
> one for each repeated measure value.
>
> Is there a quick-and-dirty way to do this transformation?
>
> Many thanks,
>
>   
There are several ways.  This is one.

 > tmp <- data.frame(id=letters[1:3], x1=1:3, x2=4:6, x3=7:9, x4=10:12)
 > tmp
  id x1 x2 x3 x4
1  a  1  4  7 10
2  b  2  5  8 11
3  c  3  6  9 12
 > reshape(tmp, direction="long", varying=list(names(tmp)[-1]),
ids="id")
    id time x1
a.1  a    1  1
b.1  b    1  2
c.1  c    1  3
a.2  a    2  4
b.2  b    2  5
c.2  c    2  6
a.3  a    3  7
b.3  b    3  8
c.3  c    3  9
a.4  a    4 10
b.4  b    4 11
c.4  c    4 12
 >