Colin,

Unless I missed something, the head function doesn't sort.  So if I have 
1000 values that match, head just gives me the first three, not the 
HIGHEST three.


[df.mydata$A=="X"&  df.mydata$C<  2,


On 8/26/09 3:01 AM, Colin Millar wrote:
> Hi,
>
> This should work - head is quite a usefull summary function
>
> head(df.mydata[df.mydata$A=="X"&  df.mydata$C<  2, ],3)
>
>
> Colin.
>
> -----Original Message-----
> From: r-help-bounces@r-project.org [mailto:r-help-bounces@r-project.org]
> On Behalf Of Noah Silverman
> Sent: 26 August 2009 10:54
> To: ottorino-luca.pantani@unifi.it
> Cc: r help
> Subject: Re: [R] Select top three values from data frame
>
>
> I only have a few values in my example, but the real data set might have
>
> 20-100 rows with A="X".  So how do I pick just the three highest ones?
>
> -N
>
>
> On 8/26/09 2:46 AM, Ottorino-Luca Pantani wrote:
>    
>> df.mydata[df.mydata$A=="X" AND df.mydata$C<  2, ]
>> will do the job ?
>>
>> 8rino
>>
>> Noah Silverman ha scritto:
>>      
>>> 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.
>>>
>>> Any suggestions?
>>>
>>>        
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