R help - Mar 2012 - Need help using Melt and cast to compute correlation for a cross tabulation

I have a data frame with a number of observed and predicted values by 
classification as shown below:

         Count   Volume  FCLASS
1      55000   60000   Grade Separated
2      43000   39000   Grade Separated
3      26000   26500   Major Arterial
4      19500   20000   Major Arterial
...

There are four classes here: Grade Separated, Major Arterial, Minor 
Arterial, and Collector

I am looking to compute the following information

FCLASS                   cor(Count,Volume)
Grade Separated   0.999
Major Arterial         0.999
Minor Arterial         0.999
Collector                 0.999

I am attempting to use the following commands to achieve this:

library(reshape)
tmp <- melt(dataframe)
cast(tmp, FCLASS ~ variable, function(Count, Volume) cor(Count, Volume))

but this is generating:  Error in is.data.frame(y) : argument "Volume"
is missing, with no default

Any suggestions?

Walter Anderson

Here is another way of doing it:
> x <- read.table(text = "       Count   Volume  FCLASS
+ 1      55000   60000   'Grade Separated'
+ 2      43000   39000   'Grade Separated'
+ 3      26000   26500   'Major Arterial'
+ 4      19500   20000   'Major Arterial'", as.is =
TRUE)
> result <- sapply(split(x, x$FCLASS), function(.grp) cor(.grp$Count,
.grp$Volume))
>
> result
Grade Separated  Major Arterial
              1               1
>

On Thu, Mar 1, 2012 at 12:23 PM, Walter Anderson
<wandrson01@gmail.com>wrote:
> I have a data frame with a number of observed and predicted values by
> classification as shown below:
>
>        Count   Volume  FCLASS
> 1      55000   60000   Grade Separated
> 2      43000   39000   Grade Separated
> 3      26000   26500   Major Arterial
> 4      19500   20000   Major Arterial
> ...
>
> There are four classes here: Grade Separated, Major Arterial, Minor
> Arterial, and Collector
>
> I am looking to compute the following information
>
> FCLASS                   cor(Count,Volume)
> Grade Separated   0.999
> Major Arterial         0.999
> Minor Arterial         0.999
> Collector                 0.999
>
> I am attempting to use the following commands to achieve this:
>
> library(reshape)
> tmp <- melt(dataframe)
> cast(tmp, FCLASS ~ variable, function(Count, Volume) cor(Count, Volume))
>
> but this is generating:  Error in is.data.frame(y) : argument
"Volume" is
> missing, with no default
>
> Any suggestions?
>
> Walter Anderson
>
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> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.

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