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t-test via matrix operations

4 messages · Kort, Eric, Brian Ripley, Pauline Gu +1 more

Original
Kort, Eric
# 
I need to calculate a large number of t statistics, and would like to do so via matrix operations.  So far I have figured out a way to calculate the mean of each row of the matrix:

d <- matrix(runif(100000,1,10), 1000, 10) # some test data
s <- rep(1,ncol(d)) # a sum vector to use for matrix multiplication
means <- (d%*%s)/ncol(d)

This is at least 1 order of magnitude faster than iterating through the rows and using the mean function (<1/100th seconds vs. 13/100th seconds on my computer).

Two questions:
1) Do you see a way to further optimize/simplify/elegantize this calculation of the row means?
2) How do I proceed to calculate the row variances with matrix operations (specifically, how can I use matrix operations to subtract each element of each row from the corresponding row mean)?

Thank you,
Eric Kort
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Brian Ripley
#
On Wed, 14 Aug 2002, Kort, Eric wrote:

            

      
      
      
    

        
rows and using the mean function (<1/100th seconds vs. 13/100th seconds
on my computer).

            

      
      
      
    

        
calculation of the row means?

function rowMeans

            

      
      
      
    

        
operations (specifically, how can I use matrix operations to subtract each
element of each row from the corresponding row mean)?

sweep does the subtraction, but I would make use of rowmeans(d^2) and
rowmeans(d) in the classic hand-calculation formula.

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Pauline Gu
    

    

      
      #
    

  


  

      
Dear R experts and Omega experts,

I am trying to run the R from Java.  Now, I am facing the problem: 
UnsatisfiedLinkError: SJava.dll, please see the detail Error message below:

Path is 
/cygdrive/c/Tcl/bin:.:/cygdrive/c/ora9iclient/jdk/jre/bin/classic:/cygdr
ive/c/Documents and 
Settings/pgu/Desktop/oldmachine/rtools:/cygdrive/e/R/gcc/bin
:/cygdrive/c/WINNT/system32:/cygdrive/c/WINNT:/cygdrive/c/WINNT/system32/WBEM:/c
ygdrive/c/ora9iclient/bin:/cygdrive/c/ora9iclient/jdk/bin:/cygdrive/c/Perl/bin:/
cygdrive/f/Mingw/bin:/cygdrive/c/Program Files/HTML Help 
Workshop:/cygdrive/e/r-
1.5.1/library/SJava/libs:/cygdrive/e/r-1.5.1/src/gnuwin32
Hello...
Exception in thread "main" java.lang.UnsatisfiedLinkError: 
E:\R-1.5.1\library\SJ
ava\libs\SJava.dll: Can't find dependent libraries
         at java.lang.ClassLoader$NativeLibrary.load(Native Method)
         at java.lang.ClassLoader.loadLibrary0(Unknown Source)
         at java.lang.ClassLoader.loadLibrary(Unknown Source)
         at java.lang.Runtime.loadLibrary0(Unknown Source)
         at java.lang.System.loadLibrary(Unknown Source)
         at 
org.omegahat.R.Java.RForeignReference.<clinit>(RForeignReference.java
:25)

As one can see, that I do have the SJava.dll directory 
(e/r-1.5.1/library/SJava/libs) in the path.  Please help.  Thanks.

OS: Window 2000
R version: R1.5.1 (compiled from Source code)
RSJava version: 0.65

Thanks in advance for your help.

Pauline

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      Brad Buchsbaum
    

    

      
      #
    

  


  

      
Pauline,

Notice your path is separated by colons, and you seem to be using windows.


Brad Buchsbaum

        
On Wed, 14 Aug 2002, Pauline Gu wrote:

        

            

      
      
      
    

        
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r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
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