On Apr 21, 2010, at 10:17 PM, gallon li wrote:
Dear r-helpers,
I have a very simple question. Suppose my data is like
id=c(rep(1,2),rep(2,2))
b=c(2,3,4,5)
m=cbind(id,b)
m
id b
[1,] 1 2
[2,] 1 3
[3,] 2 4
[4,] 2 5
I wish to select the first observation for each id. That is, I want to
quickly select two rows:
id b
1 2
2 4
> m[ !duplicated(id), ]
id b
[1,] 1 2
[2,] 2 4
only. how should i do this?
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David Winsemius, MD
West Hartford, CT
______________________________________________
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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.
