[R] help using outer function

[warthog29]

Thanks Dan. You did much more than just answer my question. 

Sincerely,


Dan Davison wrote:
> 
> On Sun, Aug 10, 2008 at 06:00:21PM +0100, Dan Davison wrote:
>> On Sun, Aug 10, 2008 at 09:02:59AM -0700, warthog29 wrote:
>> > 
>> > Hi,
>> > I would like to use the R's outer function on y below so that I can
>> subtract
>> > elements from each other. The resulting dataframe is symmetric, save
>> for the
>>                                            ^^^^^^
>> outer() returns a matrix, not a data frame.
>> 
>> > negative signs on the other half of the numbers. I would like to get
>> only
>> > half of the dataframe. Here is the code I wrote (it is returning only
>> the
>> > first line of the all elements I want. Please help). 
>> > y<-c(4,4,3.9,3.8,3.7,3.6,3.5,3.5,3.5,3.3,3.2,3.2)
>> > 
>> > b<-outer(y,y,"-")
>> 
>> > b<-as.matrix(by)
>> 
>> I assume that line was supposed to be b<-as.matrix(by). In any case
>                                  
> Hmm, I didn't really clarify things there. I meant
> b<-as.matrix(b). But anyway, not needed.
> 
>> you don't need it; b is a matrix already.
>> 
>> > # I want to keep the elements:
>> > #b[1,2:12],
>> > #b[2,3:12],
>> > #.........until
>> > #b[11,12:12].
>> 
>> Use upper.tri() to get the upper-triangle:
>> 
>>  b[upper.tri(b, diag=FALSE)]
>>  [1] 0.0 0.1 0.1 0.2 0.2 0.1 0.3 0.3 0.2 0.1 0.4 0.4 0.3 0.2 0.1 0.5 0.5
>> 0.4 0.3
>> [20] 0.2 0.1 0.5 0.5 0.4 0.3 0.2 0.1 0.0 0.5 0.5 0.4 0.3 0.2 0.1 0.0 0.0
>> 0.7 0.7
>> [39] 0.6 0.5 0.4 0.3 0.2 0.2 0.2 0.8 0.8 0.7 0.6 0.5 0.4 0.3 0.3 0.3 0.1
>> 0.8 0.8
>> [58] 0.7 0.6 0.5 0.4 0.3 0.3 0.3 0.1 0.0
>> 
>> Or perhaps you want to knock out the negative entries, but still keep the
>> matrix structure:
>> 
>>  b[lower.tri(b)] <- NA
>> 
>> or perhaps you wanted 
>> 
>> b <- abs(outer(y,y,"-"))
>> 
>> in the first place?
>> 
>> > #Here is the function I wrote to get half of matrix:
>> > 
>> > wk<-function(p){
>> > for (i in 2:p){
>> > ri<-b[i-1,i:p]
>> > return(ri)
>> > }
>> > }
>> > wk(12)
>> > #[1] 0.0 0.1 0.2 0.3 0.4 0.5 0.5 0.5 0.7 0.8 0.8
>> 
>> I think you were intending this function to be something like this
>> 
>> wk<-function(p){
>>     ri <- NULL
>>     for (i in 2:p){
>>         ri<-c(ri, b[i-1,i:p])
>>     }
>>     return(ri)
>> }
>> 
>> Note that this function will give a different result from upper.tri(),
>> because you are concatenating elements in the *rows* of the matrix,
>> whereas the way matrices are represented in R has consecutive elements
>> running down the columns. I.e. look at
>> 
>> > A <- matrix(nrow=2,ncol=2)
>> > A
>>      [,1] [,2]
>> [1,]   NA   NA
>> [2,]   NA   NA
>> > A[] <- 1:4
>> > A
>>      [,1] [,2]
>> [1,]    1    3
>> [2,]    2    4
>> 
>> Dan
>> 
>> > 
>> > As you can see, it is only returning the first line. I would like other
>> > corresponding elements too, to be found in row 2 to 12. Thanks. 
>> > -- 
>> > View this message in context:
>> http://www.nabble.com/help-using-outer-function-tp18914432p18914432.html
>> > Sent from the R help mailing list archive at Nabble.com.
>> > 
>> > ______________________________________________
>> > 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.
> 
> ______________________________________________
> 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.
> 
> 

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