[R] Using unsplit - unsplit does not seem to reverse the effect of split

[Marc Schwartz (via MN)]

On Tue, 2005-09-27 at 19:12 +0200, SÃ¸ren HÃ¸jsgaard wrote:
> In data OME in MASS I would like to extract the first 5 observations
> per subject (=ID). So I do
>  
> library(MASS)
> OMEsub <- split(OME, OME$ID)
> OMEsub <- lapply(OMEsub,function(x)x[1:5,])
> unsplit(OMEsub, OME$ID)
> 
> - which results in 
>  
> [[1]]
> [1] 1 1 1 1 1
> [[2]]
> [1] 30 30 30 30 30
> [[3]]
> [1] low low low low low
> Levels: N/A high low
> [[4]]
> [1] 35 35 40 40 45
> [[5]]
> [1] coherent   incoherent coherent   incoherent coherent  
> Levels: coherent incoherent
> [[6]]
> [1] 1 4 0 1 2
> 
> ............
>  
> [[1094]]
> [1] 4 5 5 5 2
> [[1095]]
> [1] 100 100 100 100 100
> [[1096]]
> [1] 18 18 18 18 18
> [[1097]]
> [1] N/A N/A N/A N/A N/A
> Levels: N/A high low
> There were 50 or more warnings (use warnings() to see the first 50)
> 
> warnings()
> Warning messages:
> 1: number of items to replace is not a multiple of replacement length
> 2: number of items to replace is not a multiple of replacement length
> 3: number of items to replace is not a multiple of replacement length
> ....
>  
> According to documentation unsplit is the reverse of split, but I must
> be missing a point somewhere... Can anyone help? Thanks in advance.
> SÃ¸ren


If you read the documentation for split/unsplit, you will also note that
in the Details section it says:

 'unsplit' works only with lists of vectors

as opposed to lists of data frames, which is the result of your split()
operation.

Also note that in the Value section, it indicates:

'unsplit' returns a vector for which 'split(x, f)' equals 'value'

as opposed to unsplit returning a data frame.


Thus, use:

  OME1 <- do.call("rbind", OMEsub)

where OME1 will be the result of rbind()'ing the data frames in the
OMEsub list.

See ?do.call for more information.

HTH,

Marc Schwartz