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tapply confusion

6 messages · Milan Bouchet-Valat, David Winsemius, andyspeak

andyspeak
# 
Hello
I have a huge data frame with three columns 'Roof' 'Month' and 'Temp'
i want to run analyses on the numerical Temp data by the factors Roof and
Month, separately and together.
For using more than one factor i understand i should use aggregate, but i am
struggling with the tapply for single factor analysis.
This works fine, however if i try to do anything a bit more complex, such
as:
it gives the error - Error in length(g) : 'g' is missing

What could be the problem?
Thanks




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Milan Bouchet-Valat
# 
Le mercredi 29 ao?t 2012 ? 07:37 -0700, andyspeak a ?crit :
If you read ?kruskal.test, you'll notice its default function takes (at
least) two arguments, the second being "g". Its description is:
       g: a vector or factor object giving the group for the
          corresponding elements of ?x?.  Ignored if ?x? is a list.

So you do not need tapply(): just call
kruskal.test(Temp, Roof)


The "theoretical" reason you cannot use tapply() is that it calls "FUN"
separately for each subset of the data. kruskal.test() would never be
passed the whole data set, which is needed to make a test of
differences.


Regards
David Winsemius
#
On Aug 29, 2012, at 7:37 AM, andyspeak wrote:

            

      
      
      
    

        
What is the sound of one hand clapping?

You are sending a bunch of single vectors with no grouping variable to  
a function that is expecting two data columns. Maybe you should  
explain what test you had in mind using natural language and we could  
help get you there.

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      andyspeak
    

    

      
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Hello
Thankyou for the help.

kruskal.test(Temp, Roof)   is simple but just returns one result for the
whole temperature dataset organised by roof.

I want to compare the Temp data for each Roof in each Month.  So because i
have temperature data on the three roofs for 16 different months then i want
16 separate kruskal.test results.,

How do i do this?

Thanks




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      andyspeak
    

    

      
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Actually its okay.
I just created 16 subsets of the dataframe using the different months and
then ran kruskal test 16 times.
Im sure there is a nice way to code this to do it automatically and produce
a nice table of the results but i only started learning R two weeks ago!!!

Thanks for all the help



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      David Winsemius
    

    

      
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On Aug 30, 2012, at 4:02 AM, andyspeak wrote:

        

            

      
      
      
    

        
lapply( split(dfrm, dfrm$Month), function(xfrm) {
                  kruskal.test(xfrm[["Temp"]], xfrm[["Roof"]] }

Notice that I used an assumed name for the dataframe. You have  
apparently been following unwise advice to use attach. You would be  
advised to disregard that advice.