[R] Select top three values from data frame
Mohamed Lajnef
Mohamed.lajnef at inserm.fr
Wed Aug 26 12:25:29 CEST 2009
Noah Silverman a écrit :
> 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
>
>
Hi,
and now?
df.mydata$B[order(df.mydata[df.mydata$A=="X" AND df.mydata$C < 2, ]$B)][length(df.mydata$B)-3:length(df.mydata$B)]
cheers,
ML
> 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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>
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Mohamed Lajnef
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