[R] reformatting some data

[David Winsemius]

On Dec 4, 2012, at 1:44 PM, arun wrote:

> Hi,
> You can also do this:
> dat1<-structure(list(group = c(4L, 3L, 4L, 4L, 4L, 2L),  
> X3.Hydroxybutyrate =
>  c(4e-04,
>  5e-04, 4e-04, 6e-04, 5e-04, 7e-04), X3.Hydroxyisovalerate = c(3e-04,
>  3e-04, 3e-04, 3e-04, 3e-04, 4e-04), ADP = c(5e-04, 6e-04, 6e-04,
>  5e-04, 7e-04, 7e-04)), .Names = c("group", "X3.Hydroxybutyrate",
>  "X3.Hydroxyisovalerate", "ADP"), row.names = c(347L, 353L, 359L,
>  365L, 371L, 377L), class = "data.frame")
>
> datM<-melt(dat1,id.var="group")

An explicit call to library(reshape2) might be in order before a melt  
call.

>
> xtabs(value~variable+group,data=datM)
> #                       group
> #variable                     2      3      4
>  # X3.Hydroxybutyrate    0.0007 0.0005 0.0019
>  # X3.Hydroxyisovalerate 0.0004 0.0003 0.0012
>  # ADP                   0.0007 0.0006 0.0023

This has implicitly summed the entires from items by "group" values.  
That might or might not have been what the OP wanted. xtabs does not  
allow a function to be specified. (It's output is expected to be a  
contingency table of counts so it only makes sense to sum values.) The  
aggregate function allows either choice within the base package:

I see that arun used `mean` as his function in an earlier post using  
reshape2::dcast

 > aggregate(dat1[-1] , dat1['group'], FUN=mean)
   group X3.Hydroxybutyrate X3.Hydroxyisovalerate      ADP
1     2           0.000700                 4e-04 0.000700
2     3           0.000500                 3e-04 0.000600
3     4           0.000475                 3e-04 0.000575

This is the aggregate method for summation:

 > aggregate(dat1[-1] , dat1['group'], FUN=sum)
   group X3.Hydroxybutyrate X3.Hydroxyisovalerate    ADP
1     2             0.0007                0.0004 0.0007
2     3             0.0005                0.0003 0.0006
3     4             0.0019                0.0012 0.0023

> A.K.
>
>
>
> ----- Original Message -----
> From: Charles Determan Jr <deter088 at umn.edu>
> To: r-help at r-project.org
> Cc:
> Sent: Tuesday, December 4, 2012 4:17 PM
> Subject: [R] reformatting some data
>
> Hello,
>
> I am trying to reformat some data so that it is organized by group  
> in the
> columns.  The data currently looks like this:
>
>        group X3.Hydroxybutyrate X3.Hydroxyisovalerate   ADP
> 347     4              4e-04                 3e-04                   
> 5e-04
> 353     3              5e-04                 3e-04                   
> 6e-04
> 359     4              4e-04                 3e-04                   
> 6e-04
> 365     4              6e-04                 3e-04                   
> 5e-04
> 371     4              5e-04                 3e-04                   
> 7e-04
> 377     2              7e-04                 4e-04                   
> 7e-04
>
> I would like to reformat it so it is like this:
>
>                 2          3           4
> var1
> var2
> var3
>
>
> I realize that there unequal numbers in each group but I would like to
> none-the-less if possible.
> Here is a subset of the data:
>
> structure(list(group = c(4L, 3L, 4L, 4L, 4L, 2L), X3.Hydroxybutyrate =
> c(4e-04,
> 5e-04, 4e-04, 6e-04, 5e-04, 7e-04), X3.Hydroxyisovalerate = c(3e-04,
> 3e-04, 3e-04, 3e-04, 3e-04, 4e-04), ADP = c(5e-04, 6e-04, 6e-04,
> 5e-04, 7e-04, 7e-04)), .Names = c("group", "X3.Hydroxybutyrate",
> "X3.Hydroxyisovalerate", "ADP"), row.names = c(347L, 353L, 359L,
> 365L, 371L, 377L), class = "data.frame")
>


David Winsemius, MD
Alameda, CA, USA