[R] Information on objects of "class by"
Guilherme Veiga da Rocha
gvrocha at stat.Berkeley.EDU
Thu Jul 5 18:48:54 CEST 2007
Hi all,
Does anyone know where to find more information on the "by" class?
OR
Does anyone know how to coerce an object of the "by" class into a
data.frame containing the results of FUN and the values of the
grouping variables?
OR
Does anyone know how to do the following:
I have a big table with the results of many replications of an
experiment and I want to summarize the medians according to the
experimental parameters used.
Columns 1-6 index the parameters used in that particular replication.
Column 7 is just an index to the replication number.
Column 8 is the variable I want to summarize
I did:
x=by(model.errors[, 8], model.errors[, 1:6], median)
I now have an object of class "by" that seems to contain everything
I need.
If I just output "x" to the screen, I see all I need: the median for
each unique combination of values in model.errors[, 1:6].
However, I only know how to access the information on the medians
themselves by getting x[i] where i is the index of the median I want.
The problem is:
- How do I retrieve the combination of values in model.errors[, 1:6]
for a given index "i".
OR
- How do I determine the correct index "i" for a particular
combination of the values in model.errors[, 1:6]?
Just to help the thinking: I bypassed this problem for the mean by
using lm and predict.
I could in principle do the same using the L1 loss instead of the L2
loss in lm by I do not know how to do that...
This seems a rather convoluted solution for a problem "by" is meant
to solve easily...
Any help is appreciated.
Thanks a lot,
Guilherme Rocha
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