Syntax Check: rshape2 melt()
On Thu, 27 Oct 2011, Nordlund, Dan (DSHS/RDA) wrote:
I will be leaving work shortly, and won't be able to look at this again until tomorrow some time. However, I went back and reread the help page on dcast. Here is part of that page. fun.aggregate aggregation function needed if variables do not identify a single observation for each output cell. Defaults to length (with a message) if needed but not specified.
I read that, too, Dan. But did not see how that applies to these data.
It looks like your data may be slightly different than I expected. The
fact that dcast is looking for an aggregation function suggests that you
have more than one record for some combination of site|sampdate|param. No
param value ('TDS', 'SO4', ...) should occur more than once for any
combination of site and sampdate (i.e. no multiple measures of the same
parameter on the same day in the same site). So, you might want to check
your data to make sure you have no more than 1 measurement per param per
sampdate per site.
Nope. Can't. In the database table site, date, param are the compound primary key. Besides, it makes no sense to have two concentration measurements of the same chemical on the same day from the same location. I spent a lot of time getting rid of duplicate records because the same site was listed with two spellings (one with a hyphen, one without) or some records were listed as "TDS" while others from the same day and location were entered in their spreadsheet as "Total Dissolved Solids". That table is clean, and the .csv copy didn't change any values on its way into R.
If that isn't the problem, then I would start thinking about restarting R and then re-installing reshape2. Good luck.
I'll do that tomorrow. It's sorta' a Microsoft solution: shut down computer, spin around it your chair three times, restart computer. Too bad there is not more detailed diagnostic information about the source of the error, or a way to stick a stub of code in the function call to illucidate just what dcast() thinks it sees. Thanks, Rich