[R] Odp: Select top three values from data frame

[Petr PIKAL]

Hi

r-help-bounces at r-project.org napsal dne 26.08.2009 10:36:22:

> Hi,
> 
> I'm trying to find an easy way to do this.
> 
> I want to select the top three values of a specific column in a subset 
> of rows in a data.frame.  I'll demonstrate.
> 
> A    B    C
> x    2    1
> x    4    1
> x    3    2
> y    1    5
> y    2    6
> y    3    8
> 
> 
> I want the top 3 values of B from the data.frame where A=X and C <2
> 
> I could extract all the rows where C<2, then sort by B, then take the 
> first 3.  But that seems like the wrong way around, and it also will get 

> messy with real data of over 100 columns.

One way is to use subset, order and head

head(subset(your.data[order(your.data$B, decreasing=T),], subset = C<2 & 
A=="x"), 3)

Regards
Petr


> 
> Any suggestions?
> 
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