R help - Mar 2003 - Fw: length() misbehaving?: More

With the problem below, I've discoved that
n95trt<-length(byyr$cnd95[byyr$cnd95=="tr"&!is.na(byyr$cnd95)])
does give me the correct count for the number of "tr" entries.  (The
same behavior
occurs for the "c" level of the cnd95 factor.)  It appears that
byyr$cnd95=="tr"
is finding both "tr" AND NA entries.  Is this a bug, or is it to be
expected?

Dave

Subject: length() misbehaving?

> I'm having a weird problem with length(), in R1.6.1 under windows2000. 
I have a
> dataframe called byyr, with ten columns, the first of which is named cnd95.
> summary(byyr) shows that byyr$cnd95 contains the factor level
"tr" 66 times.  Also,
> when I enter byyr$cnd95 at the command line, I can count 66 "tr"
elements in the
> resulting vector.  However, when I enter
>
> n95trt <- length(byyr$cnd95[byyr$cnd95=="tr"])
> n95trt
>
> the result is 68!  Any ideas why this is happening, and how I can fix the
miscount?
> (That column also contains 69 entries of "c", and (relevantly?)
two NA's.)
>
> Thanks for any help.
>
> Dave Parkhurst
>
>

David Parkhurst wrote:
> With the problem below, I've discoved that
>
n95trt<-length(byyr$cnd95[byyr$cnd95=="tr"&!is.na(byyr$cnd95)])
> does give me the correct count for the number of "tr" entries. 
(The same behavior
> occurs for the "c" level of the cnd95 factor.)  It appears that
> byyr$cnd95=="tr"
> is finding both "tr" AND NA entries.  Is this a bug, or is it to
be expected?
This is expected - it's an inappropriate use of length(), see my earlier 
mail.
Calculations, comparisons and indexing with NA returns NA. That's 
documented and therefore expected.

Uwe Ligges

> Dave
> 
> Subject: length() misbehaving?
> 
> 
> 
>>I'm having a weird problem with length(), in R1.6.1 under
windows2000.  I have a
>>dataframe called byyr, with ten columns, the first of which is named
cnd95.
>>summary(byyr) shows that byyr$cnd95 contains the factor level
"tr" 66 times.  Also,
>>when I enter byyr$cnd95 at the command line, I can count 66
"tr" elements in the
>>resulting vector.  However, when I enter
>>
>>n95trt <- length(byyr$cnd95[byyr$cnd95=="tr"])
>>n95trt
>>
>>the result is 68!  Any ideas why this is happening, and how I can fix
the miscount?
>>(That column also contains 69 entries of "c", and
(relevantly?) two NA's.)
>>
>>Thanks for any help.
>>
>>Dave Parkhurst
>>
>>
> 
> 
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