[R] Syntax Check: rshape2 melt()

[Rich Shepard]

On Thu, 27 Oct 2011, Nordlund, Dan (DSHS/RDA) wrote:

> I read in the sample data that you put in an earlier post.
>
>> tds.anal <- read.table('clipboard',header=TRUE)
>> tds.anal
>      site   sampdate param quant
> 1    UDS-O 2006-12-06   TDS 10800
> 4   STC-FS 1996-06-14  Cond   280
> 7    UDS-O 2007-10-04    Mg  1620
> 9    UDS-O 2007-10-04   SO4  7580
> 19 JCM-10B 2007-06-21    Ca    79
> 20 JCM-10B 2007-06-21    Cl   114

Dan,

   In your 'tds.anal' is sampdate a factor or a date? Here it's a date:

str(tds.anal)
'data.frame':	11434 obs. of  4 variables:
  $ site    : Factor w/ 143 levels "BC-0.5","BC-1",..: 134 127 134 134 73 73
91 91 91 91 ...
  $ sampdate: Date, format: "2006-12-06" "1996-06-14" ...
  $ param   : Factor w/ 7 levels "Ca","Cl","Cond",..: 7 3 4 6 1 2 4 5 1 4 ...
  $ quant   : num  10800 280 1620 7580 79 114 301 27.5 381 274 ...

   I wonder if that's what's not working here.

> Then ran the following code
>> melt(tds.anal)
> Using site, sampdate, param as id variables
>     site   sampdate param variable value
> 1   UDS-O 2006-12-06   TDS    quant 10800
> 2  STC-FS 1996-06-14  Cond    quant   280
> 3   UDS-O 2007-10-04    Mg    quant  1620
> 4   UDS-O 2007-10-04   SO4    quant  7580
> 5 JCM-10B 2007-06-21    Ca    quant    79
> 6 JCM-10B 2007-06-21    Cl    quant   114

   When I do this I see:

melt(tds.anal)
Using site, param as id variables
             site param variable     value
1          UDS-O   TDS sampdate 13488.000
2         STC-FS  Cond sampdate  9661.000
3          UDS-O    Mg sampdate 13790.000
4          UDS-O   SO4 sampdate 13790.000
5        JCM-10B    Ca sampdate 13685.000
6        JCM-10B    Cl sampdate 13685.000

   Notice there's no sampdate here.

Rich