[R] finding dedicated indexes?

[Setzer.Woodrow@epamail.epa.gov]

try d[d[,1] %in% i,]
> d[d[,1] %in% i,]
     [,1] [,2]
[1,]    5    6
[2,]   13   14
[3,]   19   20
>
R. Woodrow Setzer, Jr.                                            Phone:
(919) 541-0128
Experimental Toxicology Division                       Fax:  (919) 541-5394
Pharmacokinetics Branch
NHEERL MD-74; US EPA; RTP, NC 27711


                                                                                                                      
                    Thomas Bruns                                                                                      
                    <Thomas.Bruns at ptb.de        To:     R-help <r-help at stat.math.ethz.ch>                             
                    >                           cc:                                                                   
                    Sent by:                    Subject:     [R] finding dedicated indexes?                           
                    owner-r-help at stat.ma                                                                              
                    th.ethz.ch                                                                                        
                                                                                                                      
                                                                                                                      
                    03/20/01 10:57 AM                                                                                 
                                                                                                                      
                                                                                                                      




Hi,

I've got a matrix of two columns, say:
> d <- t(array(1:20,dim=c(2,10)))
> d
      [,1] [,2]
 [1,]    1    2
 [2,]    3    4
 [3,]    5    6
 [4,]    7    8
 [5,]    9   10
 [6,]   11   12
 [7,]   13   14
 [8,]   15   16
 [9,]   17   18
[10,]   19   20

now I need those values from column #2 where column #1 is equal to
certain values. eg.:
> i <- c(13,5,19)
The following doesn't work but you may get the idea:
>print( d[ d[,1]==i ,2])

It is possible to do it with a loop:
> k <- i        # just to allocate k
> for (j in 1:3) {k[j] <- which(d[,1]==i[j]))}
> print(d[k,2])

But I believe there has to be a more efficient way in R without explicit
loops, which I don´t know by now ???

Tia.

Thomas


--
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Dr. Thomas Bruns                  <thomas.bruns at ptb.de>

         Physikalisch-Technische Bundesanstalt
                      Braunschweig
Fachlabor: 1.13
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D-38116 Braunschweig              Fax: 0531/592-69-1132
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