[R] Analyzing large transition matrix

[Bill Harris]

Let's say you have a dataframe of car trade-ins.  For example, each row
contains 

oldcar   newcar   qty

and a typical entry could be

lexus   bmw    1

I put the qty column to allow for fleet purchases, where one purchase
may convert multiple cars at once.

I'd like to show what's going on.  I could do a histogram of newcar to
show the frequency each type of car is bought.  If there are 5-10 car
types, that works.  If there are 50-100 or more, the legend gets
illegible.

I could also do a histogram of oldcar to see what people gave up, but
that's less interesting.

I'm considering a correlogram using the corrgram package, but a heat map
might work, too.  Any tips on making the legends useful in any of this?
Any better approaches to try?

I tried table() and prop.table() to see if I could get transition
probabilities as if this were a Markov chain, but dim() comes out 108
78, which is still too big to print or visualize.

Suggestions?

Thanks,

Bill
-- 
Bill Harris                  http://makingsense.facilitatedsystems.com/
Facilitated Systems                              Everett, WA 98208 USA
http://www.facilitatedsystems.com/               phone: +1 425 374-1845