NA in table with integer types

OK.  Thanks.  So, if you use table() on a factor that contains NA's, but
for which NA is not a level, is there any way to get table to generate an
entry for the NAs?  For example, in below, even "exclude=NULL" will not
give me an entry for <NA> on the factor y:

x <- c(1,2,3,3,NA)
y <- factor(x)
y

[1] 1    2    3    3    <NA>
Levels: 1 2 3

table(y,exclude=NA)

y
1 2 3
1 1 2

table(y,exclude=NaN)

y
1 2 3
1 1 2

table(y,exclude=NULL)

y
1 2 3
1 1 2

On Fri, 8 Apr 2005, Prof Brian Ripley wrote:

NaN only applies to double values: there is no integer NaN (nor Inf nor
-Inf).  The difference is clear from

factor(x, exclude=NaN)

[1] 1    2    3    3    <NA>
Levels: 1 2 3 <NA>

factor(as.integer(x), exclude=NaN)

[1] 1    2    3    3    <NA>
Levels: 1 2 3

If you read ?factor it says

  exclude: a vector of values to be excluded when forming the set of
           levels. This should be of the same type as 'x', and will be
           coerced if necessary.

and as.integer(NaN) is integer NA.  So  factor(as.integer(x), exclude=NaN)
is the same as  factor(as.integer(x), exclude=NA).

[rest deleted]

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