[R] "Glueing" factors together

(Ted Harding) Ted.Harding at nessie.mcc.ac.uk
Tue Jun 15 10:26:06 CEST 2004

Hi folks,

Suppose I have a series of cases each with categorical
factors A, B.

What is the best way to "glue" A and B together into a single
factor? For example, given

A0 B1 ...
A1 B1 ...
A0 B2 ...
A1 B0 ...
A0 B0 ...
A1 B2 ...

then I'd like to end up with a single factor with levels

  A0B0, A0B1, A0B2, A1B0, A1B1, A1B2

according to all the combinations which actually occur in the
data (e.g. if (A1,B2) did not occur in the data, then A1B2 would
not be a level in the resulting "glued" factor).

I can see clumsy and tedious ways involving manipulating strings,
paste(), etc.; but I'm sure it must be possible more elegantly.

With thanks, and best wishes to all,

E-Mail: (Ted Harding) <Ted.Harding at nessie.mcc.ac.uk>
Fax-to-email: +44 (0)870 167 1972
Date: 15-Jun-04                                       Time: 09:26:06
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