[R] person-level to person-period xfm

[David Winsemius]

On Nov 19, 2009, at 12:23 PM, Richard M. Heiberger wrote:

> 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.

Here's another:
 > data.frame(id=tmp$id, stack(tmp, select=-id))
    id values ind
1   a      1  x1
2   b      2  x1
3   c      3  x1
4   a      4  x2
5   b      5  x2
6   c      6  x2
7   a      7  x3
8   b      8  x3
9   c      9  x3
10  a     10  x4
11  b     11  x4
12  c     12  x4


>
> > 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
> >
>
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT