[R] weird apply() behavior

[David Winsemius]

On Aug 29, 2011, at 8:17 PM, David Winsemius wrote:

>
> On Aug 29, 2011, at 8:02 PM, array chip wrote:
>
>> Hi, I had a weird results from using apply(). Here is an simple  
>> example:
>>
>>> y<-data.frame(list(a=c(1,NA),b=c('2k','0')))
>>> y
>>
>>    a     b
>> 1  1   2k
>> 2 NA   0
>>
>>> apply(y,1,function(x){x<-unlist(x);
>
> That is quite unnecessary since apply coerces the rows into vectors  
> whether you want it to or not,
>
>>> if (!is.na(x[2]) & x[2]=='2k' & !is.na(x[1]) & x[1]=='1') 1 else  
>>> 0} )
>
> So everything get coerced to character and I suspect NA -> "NA" or  
> NA_character and so !is.na() gives the wrong result. Try printing  
> str(x) inside that apply loop.

I was wrong abut my diagnosis but my methods were sound.
This is str from the first row:
Named chr [1:2] " 1" "2k"

So probably the default stringsAsFactors rule created "b" as a factor  
and something else made that integer `1` turn into " 1" .

-- 
DA\avid.


>
> -- 
> David.
>
>
>
>>
>> This should print "1 0" as output, as demonstrated by:
>>
>>> apply(y[1,],1,function(x){x<-unlist(x); if (!is.na(x[2]) &  
>>> x[2]=='2k' & !is.na(x[1]) & x[1]=='1') 1 else 0} )
>> 1
>> 1
>>> apply(y[2,],1,function(x){x<-unlist(x); if (!is.na(x[2]) &  
>>> x[2]=='2k' & !is.na(x[1]) & x[1]=='1') 1 else 0} )
>> 2
>> 0
>>
>>
>> But it actually prints:
>>
>>> apply(y,1,function(x){x<-unlist(x); if (!is.na(x[2]) & x[2]=='2k'  
>>> & !is.na(x[1]) & x[1]=='1') 1 else 0} )
>>
>> [1] 0 0
>>
>>
>> Anyone has any suggestion?
>>
>> Thanks
>>
>> John
>>
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> David Winsemius, MD
> West Hartford, CT
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
West Hartford, CT