[R] Why does aggregate fail?

[James Rome]

On 2/7/2010 1:35 PM, David Winsemius wrote:But to answer your question:

> apply(d, 1, function(z) aggregate(z, by=list(s), FUN=sum) )

David,

That works, but I do not understand why I could not use aggregate
directly. And the answer comes out as a list, which thus far baffles me.
How do I get the answer as a matrix in my original code, which I
modified to use apply?

ha = matrix(nrow=7, ncol=24)
colnames(ha) = as.character(c(0:23))
rownames(ha) = rownames(maxrdf)
for(j in 1:7) {
    x = apply(maxrdf[j,], 1, function(z) aggregate(z, by=list(s),
FUN=sum) )           
    ha[j,] = x[[1]][2]   
}

Unfortunately, ha gets converted into a list, and then I can't use it
for my plots. And you can probably educate me on how to get what I am
aiming for (a matrix with the rows as the days, the columns as the
hours, and the content as the hourly sum of the 15-minute chunks)
without using the above for loop.

Thanks for the help,
Jim