[R] omit empty cells in crosstab?

[Peter Dalgaard]

Dieter Menne wrote:
> sjaffe <sjaffe <at> riskspan.com> writes:
> 
>> I have data with many factors, each taking many values. However, only
>> relatively few combinations appear in the data, ie have nonzero counts, in
>> other words the resulting table is sparse. Say we have 10 factors each with
>> 10 levels. The result of table() would exceed the memory space (on a 32bit
>> machine). Is there any way to produce a table with empty cells omitted?
>> (without first producing the whole table and then removing rows.)
> 
> It would be easier if you had a reproducible base example, but I 
> suggest to create ONE new factor of the pasted levels using unique(), 
> and  creating a table of these.

interaction(..., drop=TRUE) may be a neater way.

-- 
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