[R] problems subsetting

[David Winsemius]

On Nov 18, 2010, at 10:25 AM, Martin Tomko wrote:

> Hi Gerrit,
> indeed, that works. Excellent tip!
>
> For reference, I did this:
>
> subset1<-subset(summarystats,(Type==1)&(Class==1)&(Category==1))
>
> I am still not totally sure when one uses "&" amd when "&&"  - I was  
> under the impression that && stands for logical AND....

Both stand for logical AND. "&" is used for vectorized comparisons,  
while "&&" will only compare the first elements of the two sides  
(usually, but apparently not always) with a warning if there are  
longer objects than expected.

 > c(1,0,1,0,1) & c(0,0,1,1,-1)
[1] FALSE FALSE  TRUE FALSE  TRUE

 > c(1,0,1,0,1) && c(0,0,1,1,-1)
[1] FALSE

 > c(1,0,1,0,1) && c(1,0,1,1,-1)
[1] TRUE

-- 
David.

>
> Thanks a lot.
>
>
> Martin
>
> On 11/18/2010 3:58 PM, Gerrit Eichner wrote:
>> Hello, Martin,
>>
>> as to your first problem, look at function subset(), and  
>> particularly at its argument "subset".
>>
>> HTH,
>>
>> Gerrit
>>
>>
>> On Thu, 18 Nov 2010, Martin Tomko wrote:
>>
>>> Dear all,
>>> I have searched the forums for an answer - and there is plenty of  
>>> questions along the same line - but none of the paproaches shown  
>>> worked to my problem:
>>>
>>> I have a data frame that I get from a csv:
>>>
>>> summarystats<-as.data.frame(read.csv(file=f_summary));
>>>
>>> where I have the columns Dataset, Class, Type, Category,..
>>> Problem1:  I want to find a subset of this frame, based on values  
>>> in multiple columns
>>> What I do currently is:
>>>
>>> subset1 <- summarystats
>>> subset1<-subset1[subset1$Class == 1,]
>>> subset1<-subset1[subset1$Type == 1,]
>>> subset1<-subset1[subset1$Category == 1,]
>>>
>>> Now, this works, but is UGLY! I tried using "&&" or "&" , for  
>>> isntance : subset1<-subset1[ (subset1$Class == 1)&&  
>>> (subset1$Category == 1),]
>>> but it returns an empty data frame.
>>>
>>> Anyway, the main problem is
>>> Problem2:
>>> I have a second data frame - a square matrix (rownames ==  
>>> colnames), distm:
>>>
>>> distm<-read.table(file=f_simmatrix, sep = ",");
>>> what I want is select ONLY the columns and rows entries matching  
>>> the above subset1:
>>>
>>> subset2<-distm[subset1$Dataset,subset1$Dataset] returns a matrix  
>>> of correct size, but with incorrect entries (established by visual  
>>> inspection).
>>>
>>> this is the same as:
>>> selectedrows<-as.vector(subset1$Dataset)
>>> subset2<-distm[selectedrows,selectedrows]
>>>
>>> also verified using:
>>> rownames(subset2)%in% selectedrows
>>> [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE  
>>> FALSE FALSE
>>> [13] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE  
>>> FALSE FALSE
>>> [25] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE  
>>> FALSE FALSE
>>> [37] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
>>>
>>> What am I missing?
>>>
>>> Thanks
>>> Martin
>>>
>>> ______________________________________________
>>> 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.
>>>
>>
>> ---------------------------------------------------------------------
>> AOR Dr. Gerrit Eichner               Mathematical Institute, Room 212
>> gerrit.eichner at math.uni-giessen.de   Justus-Liebig-University Giessen
>> Tel: +49-(0)641-99-32104          Arndtstr. 2, 35392 Giessen, Germany
>> Fax: +49-(0)641-99-32109        http://www.uni-giessen.de/cms/eichner
>> ---------------------------------------------------------------------
>>
>
>
> -- 
> Martin Tomko
> Postdoctoral Research Assistant
>
> Geographic Information Systems Division
> Department of Geography
> University of Zurich - Irchel
> Winterthurerstr. 190
> CH-8057 Zurich, Switzerland
>
> email: 	martin.tomko at geo.uzh.ch
> site:	http://www.geo.uzh.ch/~mtomko
> mob: 	+41-788 629 558
> tel: 	+41-44-6355256
> fax: 	+41-44-6356848
>
> ______________________________________________
> 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