[R] Unique Pairs based on a Minimum Value

[Chuck Cleland]

Bret Collier wrote:
> RUsers,
> 
> I am trying (with little success) to determine how to combine unique and 
> min to do some data frame manipulations and I could use a little advice. 
>   I have tried various combinations of 'unique', 'min' and 'apply' with 
> no luck.
> 
> Given this simple example data (x, y)
> 
> x<-c(10, 10, 12, 13, 15, 16 ,17, 17, 17)
> y<-c(112, 117, 111, 117, 114, 113, 119, 121, 130)
> 
> as.data.frame(cbind(x, y))
> 
>     x   y
> 1 10 112
> 2 10 117
> 3 12 111
> 4 13 117
> 5 15 114
> 6 16 113
> 7 17 119
> 8 17 121
> 9 17 130
> 
> I have been attempting to get all those unique 'x-y' combinations for 
> which the y column is the minimum of the values y takes for each unique 
> x (ID variable), such as below.
> 
>     x   y
> 1 10 112
> 3 12 111
> 4 13 117
> 5 15 114
> 6 16 113
> 7 17 119
> 
> Any advice/directions I could look would be appreciated.

x<-c(10, 10, 12, 13, 15, 16 ,17, 17, 17)
y<-c(112, 117, 111, 117, 114, 113, 119, 121, 130)
df <- data.frame(x,y)

aggregate(df, list(df$x), min)[,c("x","y")]
   x   y
1 10 112
2 12 111
3 13 117
4 15 114
5 16 113
6 17 119

> TIA,
> Bret
> R 2.6.0; platform i386-pc-mingw32
> 
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-- 
Chuck Cleland, Ph.D.
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