R help - Jun 2005 - Convert a "by" list into a data frame

Dear useRs,

Is there a way to convert a list generated by "by" command into a data
frame?
Or, more generally, are there any functions that operate on "by"
lists?
My "by" list consists of numeric vectors of equal length and the
objective is
to calculate the sum of the same index elements (i.e., column-wise sums). For
example, if the "by" list were

--------------------------
Data_DF$CASE: 1
       IVTT     COST
[1,]     1        2
--------------------------
Data_DF$CASE: 2
       IVTT     COST
[1,]     2        4
---------------------------

I would like to finally obtain a numeric vector:

result
[1]  1.5   3

Thank you.

--
Tudor Dan Bodea
Georgia Institute of Technology
School of Civil and Environmental Engineering

On 6/26/05, Tudor Bodea <gtg757i at mail.gatech.edu>
wrote:
> Dear useRs,
> 
> Is there a way to convert a list generated by "by" command into a
data frame?
Here is an example which creates a by object whose elements
are the first row of each Species of iris.  The next line converts
that to a data frame:

   by.object <- by(iris, iris$Species, head, 1)
   do.call("rbind", by.object)