[R] (newbie) Accessing the pieces of a 'by' object

[Gabor Grothendieck]

Sorry, that should be:

iris.by <- by(iris[,-5], iris[,5,drop=FALSE],colSums)
do.call("rbind", iris.by)

On 3/7/06, Gabor Grothendieck <ggrothendieck at gmail.com> wrote:
> Try this:
>
> iris.by <- do.call("rbind", by(iris[,-5], iris[,5,drop=FALSE],colSums))
> do.call("rbind", iris.by)
>
> On 3/7/06, Vivek Satsangi <vivek.satsangi at gmail.com> wrote:
> > Folks,
> > I know that I can do the following using a loop. That's been a lot
> > easier for me to write and understand. But I am trying to force myself
> > to use more vectorized / matrixed code so that eventually I will
> > become a better R programmer.
> >
> > I have a dataframe that has some values by Year, Quarter and Ranking.
> > The variable of interest is the return (F3MRet), to be weighted
> > averaged within the year, quarter and ranking. At the end, we want to
> > end up with a table like this:
> > year  quarter ranking1 ranking2 ... ranking10
> > 1987 1 1.33 1.45 ... 1.99
> > 1987 2 6.45 3.22 ... 8.33
> > .
> > .
> > 2005 4 2.22 3.33 ... 1.22
> >
> > The dataset is too large to post and I can't come up with a small
> > working example very easily.
> >
> > I tried the Reshape() package and also the aggregate and reshape
> > functions. Those don't work too well becuase of the need to pass
> > weighted.mean a weights vector. I tried the by() function, but now I
> > don't know how to coerce the returned object into a matrix so that I
> > can reshape it.
> >
> > > fvs_weighted.mean <- function(y) weighted.mean(y$F3MRet, y$IndexWeight, na.rm=T);
> > > tmp_byRet <- by(dfReturns,
> >     list(dfReturns$Quarter,dfReturns$Year,dfReturns$Ranking),
> >     fvs_weighted.mean);
> >
> > And various other ways to get the tmp_byRet object into a matrix were
> > tried, eg. unlist(), a loop like this:
> > dfRet <- data.frame(tmp_byRet);
> > for(i in 1:dim(dfRet)[2]){
> >       dfRet[ ,i] <- as.vector(dfRet[ ,i]);
> > }
> > In each case, I got some error or the other.
> >
> > So, please help me get unstuck. How can I get the tmp_byRet() object
> > into a matrix or a dataframe?
> >
> > --
> > -- Vivek Satsangi
> > Rochester, NY USA
> > "No amount of sophistication is going to allay the fact that all your
> > knowledge is about the past and all your decisions are about the
> > future." -- Ian Wilson
> >
> > ______________________________________________
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> >
>