[R] Compact Indicator Matrices

[Douglas Bates]

On Sat, May 10, 2008 at 5:27 AM, amarkos <amarkos at gmail.com> wrote:
> An indicator matrix is a binary matrix with orthogonal columns whose
> rows sum to 1. A row of this matrix could be [0 1 0 0]. My problem is
> to group the similar rows (profiles) so that to create a compact form
> of the matrix.

I'm not sure exactly what you mean by a compact form of this matrix.
Do you mean that you want to collapse similar rows into a single row
and perhaps a count of the number of times that this row occurs?

In R indicator matrices are typically generated from a factor and
essentially you are asking for the tabulation of the factor, such as
provided by the functions table and xtabs.

> Is there an R function that deals with this problem or do I have to
> write it from scratch?
>
> Thanks,
> Angelos Markos
> Dr. Applied Informatics,
> University of Macedonia, Greece
>
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