[R] Displaying Counts of Unused Factors in Contingency Tables with table()

[ntyson at clovermail.net]

Dennis,

Thank you for your response.  For clarification, I was not expecting  
table() to divinely figure out the intent that I was making two levels  
out of one (given my character vectors).  Since table() is a generic  
function that behaves differently with character and factor vectors, I  
needed a way to convert the data I had to get the desired behavior.   
Your factor() statements will accomplish my goal of putting zeros into  
contingency tables.

Regards,

Na'im


Quoting "Dennis Murphy" <djmuser at gmail.com>:

> Hi,
>
> table() is behaving as documented with respect to your example. local.labels
> is a *character* vector with two distinct values and local.preds is a
> *character* variable with one distinct value. If you were expecting your
> table to divine that you wanted to include 'ah~' as a missing value in your
> local.preds object, it's not going to happen under your current setup.
>
>> local.labels <- c("ah", "ah", "ah~")
>> local.preds <- c("ah", "ah", "ah")
>> table(local.labels, local.preds)
>             local.preds
> local.labels ah
>          ah   2
>          ah~  1
>> class(local.labels)
> [1] "character"
>> class(local.preds)
> [1] "character"
>
>
> Is this what you had in mind?
>
> labels <- factor(local.labels)
> preds <- factor(local.preds, levels = c('ah', 'ah~'))
>> table(labels, preds)
>       preds
> labels ah ah~
>    ah   2   0
>    ah~  1   0
>
>> labels
> [1] ah  ah  ah~
> Levels: ah ah~
>> preds
> [1] ah ah ah
> Levels: ah ah~
>
> There is a distinction in R between character objects and factor objects.
> More generally, many [generic] functions behave differently depending on the
> type of object(s) supplied as input.
>
> HTH,
> Dennis
>
> On Wed, Jul 28, 2010 at 10:29 PM, Na'im R. Tyson  
> <ntyson at clovermail.net>wrote:
>
>> R-philes,
>>
>> I have a question about displaying counts of unused factors using the
>> table() function.  I have two vectors with character data in them:
>>
>> local.labels("ah", "ah", "ah~")
>> local.preds("ah", "ah", "ah")
>>
>> If I use the table function as shown below, I get an error because the
>> number of levels do not match up.
>>
>> v.cont.table <- table(local.labels, local.preds, dnn=c("observed",
>> "predicted"));
>>
>> Is there any way to get zero counts into the contingency table, or would I
>> have to use a flat table?  Any help with sample code, or a pointer to a
>> previous post, would be much appreciated.
>>
>> Regards,
>>
>> Na'im
>>
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>