[R] Efficient way to repeat rows (or columns) of a matrix?

[Talbot Katz]

Brilliant, thanks!

--  TMK  --
212-460-5430	home
917-656-5351	cell



>From: "James W. MacDonald" <jmacdon at med.umich.edu>
>To: Talbot Katz <topkatz at msn.com>
>CC: r-help at stat.math.ethz.ch
>Subject: Re: [R] Efficient way to repeat rows (or columns) of a matrix?
>Date: Wed, 28 Feb 2007 18:20:32 -0500
>
>Hi Talbot,
>
>ma <- matrix(1:6, nrow  = 2)
>rma <- ma[rep(1:2, c(2,3)),]
>
>Best,
>
>Jim
>
>
>
>Talbot Katz wrote:
>>Hi.
>>
>>If I have a vector, v_1, and another vector of positive integers, i_1, the 
>>same length as v_1, then rep(v_1,i_1) will repeat v_i[j] exactly i_1[j] 
>>times, like so:
>>
>>
>>>rep(c(1,2,3),c(3,2,1))
>>
>>[1] 1 1 1 2 2 3
>>
>>
>>I'd like to do the same sort of thing where I replace v_1 with a matrix, 
>>and the jth row of the matrix is repeated i_1 times.
>>
>>Obviously, I could do this with for loops, like the following:
>>
>>
>>>(ma1=matrix(1:6,nrow=2))
>>
>>      [,1] [,2] [,3]
>>[1,]    1    3    5
>>[2,]    2    4    6
>>
>>>vr1=c(2,3)
>>>rma1=NULL
>>>for(i in 1:length(vr1)){for(j in 1:vr1[i]){rma1=rbind(rma1,ma1[i,])}}
>>>rma1
>>
>>      [,1] [,2] [,3]
>>[1,]    1    3    5
>>[2,]    1    3    5
>>[3,]    2    4    6
>>[4,]    2    4    6
>>[5,]    2    4    6
>>
>>
>>I just thought some of you clever programmers could show me a more 
>>efficient way.  (I apologize if this question has come up before and 
>>you're tired of answering it ;-)
>>
>>Thanks!
>>
>>--  TMK  --
>>212-460-5430	home
>>917-656-5351	cell
>>
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>>and provide commented, minimal, self-contained, reproducible code.
>
>
>--
>James W. MacDonald
>University of Michigan
>Affymetrix and cDNA Microarray Core
>1500 E Medical Center Drive
>Ann Arbor MI 48109
>734-647-5623
>
>
>
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