one way is the following:
a1 <- c(9,8,rep(NA,5))
a2 <- c(3,NA,3,NA,3,NA,4)
a3 <- c(11,6,7,NA,5,NA,6)
M <- rbind(a1,a2,a3)
ind <- !is.na(M)
tapply(M[ind], row(M)[ind], tail, 1)
I hope it helps.
Best,
Dimitris
On 4/20/2010 10:33 AM, gallon li wrote:
I have a matrix of the following form:
time
id 0 2 4 6 9 12 14
3 9 8 NA NA NA NA NA
7 3 NA 3 NA 3 NA 4
13 11 6 7 NA 5 NA 6
.....
I hope for each row to select the last observation which is not 'NA'.
For example, for the first row, id=3, the value I want to select is 8
for the second row, id=7, the value I want to select is 4
for the third row, id=13, the value I want to select is 6
....
if it would be easier for you to demonstrate for me, here I include the code
to generate the above three-row matrix:
a1=c(9,8,rep(NA,5))
a2=c(3,NA,3,NA,3,NA,4)
a3=c(11,6,7,NA,5,NA,6)
matrix=rbind(a1,a2,a3)
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--
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center
Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
Fax: +31/(0)10/7043014
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
