[R] function to populate a matrix based on a lookup to another matrix ?

[peter leonard]

That worked perfect. Thanks for the fast response.

Peter Leonard


>From: Uwe Ligges <ligges at statistik.uni-dortmund.de>
>To: peter leonard <pfleonard at hotmail.com>
>CC: r-help at stat.math.ethz.ch
>Subject: Re: [R] function to populate a matrix based on a lookup to another 
>matrix ?
>Date: Sat, 31 May 2003 17:58:27 +0200
>
>peter leonard wrote:
>>Hi,
>>
>>This is a beginner R question.
>>
>>I have a  4x4 matrix  named 'lookup' with the following values:
>>
>>            1         2               3          4
>>1 0.000000 2.828427 5.656854 8.485281
>>2 2.828427 0.000000 2.828427 5.656854
>>3 5.656854 2.828427 0.000000 2.828427
>>4 8.485281 5.656854 2.828427 0.000000
>>
>>I then create a new empty matrix named 'dd' with specfic row and col names 
>>:
>>
>>   1   3   4   3    3   1
>>1 NA NA NA NA NA NA
>>2 NA NA NA NA NA NA
>>3 NA NA NA NA NA NA
>>4 NA NA NA NA NA NA
>>3 NA NA NA NA NA NA
>>2 NA NA NA NA NA NA
>>1 NA NA NA NA NA NA
>>
>>I want to be able populate the cells in 'dd' using 'lookup' based on the 
>>specified rownames and colnames of 'dd'. For example, the cell in 'dd' 
>>where the rowname =2 and the colname = 1 should be assigned the value 
>>2.828427 .
>>
>>I've tried several ways of doing this with the apply function  but without 
>>success. I can do it with a for loop but I want to avoid that for 
>>efficiency reasons.
>>
>>After running the function, as an example, the first column of 'dd' should 
>>look like this :
>>
>>             1
>>1 0.000000000
>>2 2.828427125
>>3 5.656854249
>>4 8.485281374
>>3 5.656854249
>>2 2.828427125
>>1 0.000000000
>>
>>Can anyone please help me identify the required function or an alternative 
>>way of achieving the same result? Hopefully this is simple and I'm just 
>>not seeing it.
>>
>>Thanks
>>Peter
>>
>
>  dd <- lookup[as.numeric(rownames(dd)), as.numeric(colnames(dd))]
>and after that restoring dd's row- and colnames.
>
>Anyway, I guess you don't need to create "dd". Just calculate those 
>rownames (rn) and colnames (cn) as integers. Then the following works:
>
>  dd <- lookup[rn, cn]
>
>Uwe Ligges
>