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need help with chisq

4 messages · David Winsemius, Stephanie Kovalchik, JC

JC
# 
I am very new to R. I have some data from a CVS stored in vdata with 4
columns labeled:
X08, Y08, X09, Y09.

I have created two new "columns" like so:

Z08 <- (vdata$X08-vdata$Y08)

Z09 <- (vdata$X09-vdata$Y09)

I would like to use chisq.test for each "row" and output the p-value
for each in a stored variable. I don't know how to do it. Can you
help?

so far I have done it for one row (but I want it done automatically
for all my data):

chidata=rbind(c(vdata$Y08[1],Z08[1]),c(vdata$Y09[1],Z09[1]))
results <- chisq.test(chidata)
results$p.value

I tried removing the [1] and the c() but that didn't work...  Any
ideas?

THANKS!
David Winsemius
#
On May 9, 2009, at 4:53 PM, JC wrote:

            

      
      
      
    

        
Of what?

            

      
      
      
    

        
Maybe I am dense, but I cannot figure out what hypothesis is being  
tested.

            

      
      
      
    

        
Generally using apply(vdata, 1, ..... would give you a row by row  
computation.

            

      
      
      
    

        
As Jim Holtman's tag line says: "What problem are you trying to solve?"

David Winsemius, MD
Heritage Laboratories
West Hartford, CT

  
  


  


      

    

    

      
      

        


  

        

      Stephanie Kovalchik
    

    

      
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JC,

If each row are the counts for a 2 x 2 contingency table - so for the  
ith contingency table you have counts for row 1 c(Y08[i],Z08[i]) and  
row 2 (Y09[i],Z09[i]) then you could use apply:

X <- cbind(vdata$Y08,vdata$X08-vdata$Y08,vdata$Y09,vdata$X09-vdata$Y98)

f.chisq <- function(x){
m <- matrix(x,2,2)
chisq.test(m)$p.value
}

apply(X,1,f.chisq)



Quoting JC <jerome.coste at gmail.com>:

            

      
      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        


  

        

      JC
    

    

      
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Thank you Stephanie. This is perfect!

        
On May 10, 12:34?pm, Stephanie Kovalchik <sko... at ucla.edu> wrote: