[R] pairwise comparisions

[David Winsemius]

On Sep 10, 2012, at 11:03 AM, David Winsemius wrote:

> 
> On Sep 10, 2012, at 7:00 AM, priya wrote:
> 
>> Hi ,
>> I am new to R .
> 
> How new? Is this still in a file? ... or has it been imported to an R object. If it really still is in a file,  then Bert's suggestion of first reading "Intro to R" rather than posting to R help is on point. If it is an R object, you _should_ have used dput(head(obj)) to provide an appropriate test case for solutions.
> 
>> I am facing difficulty how to make pairwise comparisions.
>> For example. I have a file which looks like below
>>  a b c d
>> x  3 6 7 6
>> y  7 8 6 5
>> z  5 4 7 8
>> Here I need to look for the each pairwise comparisions (ab,ac,ad,bc,bd,cd
>> for each row)
> 
> Let's assume it's in a matrix of data.frame named X. To get pairwise combinations try:
> 
> CX <- combn( colnames(X), 2)
> 
> That's going to be a 2 row character matrix. Perhaps this will work but since you provide not example it will remain untested.
> 
> apply(CX, 2, function(comb), pmin(X[, comb[1]], X[, comb[2]] ) )

The virtues of testing herein demonstrated. There is an inappropriately placed comma right after function(comb)

> X <- read.table(text=" a b c d
+ x  3 6 7 6
+ y  7 8 6 5
+ z  5 4 7 8", header=TRUE)

> CX <- combn( colnames(X), 2)
> 
> apply(CX, 2, function(comb)  pmin(X[, comb[1]], X[, comb[2]] ) )
     [,1] [,2] [,3] [,4] [,5] [,6]
[1,]    3    3    3    6    6    6
[2,]    7    6    5    6    5    5
[3,]    4    5    5    4    4    7

> 
>> For instance ,looking at first row, for x i need to look for ab values and
>> take the min(3,6) >5 ,if its satistfies the count should be noted, (now
>> count is 0), bc values ,min(6,7) >5 ,count for x =1 etc. Likewise all the
>> comparisons are made and count is noted for x,y,z. 
>> Is there any function to make pairwise comparisions in R or any easy way to
>> do this?
>> Any help is greatly appreciated. 
> -- 
> 

David Winsemius, MD
Alameda, CA, USA