[R] reshape with two time variables

[Peter Dalgaard]

hadley wickham wrote:
> On Fri, Jan 30, 2009 at 5:57 PM, Neil Stewart
> <neil.stewart at warwick.ac.uk> wrote:
>> I have a data frame in wide format that I'd like to convert to long format.
>> For example, in wide format I have:
>>
>>        id      A1B1    A1B2    A2B1    A2B2
>> 1       1       400     475     420     510
>> 2       2       390     500     470     472
>> 3       3       428     512     555     610
>> 4       4       703     787     801     822
>> 5       5       611     634     721     705
>> 6       6       543     522     612     788
>> 7       7       411     488     506     623
>> 8       8       654     644     711     795
>>
>> A is one repeated-measures variable with levels 1 and 2. B is a second
>> repeated-measures variable also with levels 1 and 2. I'd like to end up
>> with:
>>
>>        id      A       B       value
>> 1       1       1       1       400
>> 2       2       1       1       390
>> 3       3       1       1       428
>> 4       4       1       1       703
>> 5       5       1       1       611
>> 6       6       1       1       543
>> 7       7       1       1       411
>> 8       8       1       1       654
>> 9       1       1       2       475
>> 10      2       1       2       500
>> 11      3       1       2       512
>> 12      4       1       2       787
>> 13      5       1       2       634
>> 14      6       1       2       522
>> 15      7       1       2       488
>> 16      8       1       2       644
>> 17      1       2       1       420
>> 18      2       2       1       470
>> 19      3       2       1       555
>> 20      4       2       1       801
>> 21      5       2       1       721
>> 22      6       2       1       612
>> 23      7       2       1       506
>> 24      8       2       1       711
>> 25      1       2       2       510
>> 26      2       2       2       472
>> 27      3       2       2       610
>> 28      4       2       2       822
>> 29      5       2       2       705
>> 30      6       2       2       788
>> 31      7       2       2       623
>> 32      8       2       2       795
>>
>> I've been working with reshape and with the reshape package, but with no
>> success for the two-time-variable case. Can anyone help please?
> 
> If you're using melt from the reshape package, once you've melted the
> data, you'll need to do something like:
> 
> m$a <- as.numeric(substr(m$variable, 1, 1))
> m$b <- as.numeric(substr(m$variable, 3, 3))
> m$variable <- NULL

Also, things like this should work (here using stock reshape):

 > xx <- reshape(x, direction="long", varying=2:5, v.names="val")
 > cbind(xx, expand.grid(B=1:2,A=1:2)[xx$time,])
     id time val B A
1.1  1    1 400 1 1
2.1  2    1 390 1 1
3.1  3    1 428 1 1
4.1  4    1 703 1 1
5.1  5    1 611 1 1
6.1  6    1 543 1 1
7.1  7    1 411 1 1
8.1  8    1 654 1 1
1.2  1    2 475 2 1
2.2  2    2 500 2 1
3.2  3    2 512 2 1
4.2  4    2 787 2 1
5.2  5    2 634 2 1
...

Once you got your mind wrapped around it, the pattern might be easier to 
generalize to more complex within-subject designs.


-- 
    O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
   c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
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~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)              FAX: (+45) 35327907