[R] Extract Row on Criteria

[David Winsemius]

On Mar 5, 2009, at 10:38 PM, David Winsemius wrote:

> See if this gets you further along:
>
> ?order
> ?rev
> ?"["
>
> > df <- data.frame(x = 1:20, rsamp = sample(1:20,20), Lets  
> =LETTERS[1:20])
> > ord <- order(df$rsamp)
> # creates a sorted vector of row numbers
> > df[ord,]
>    x rsamp Lets
> 16 16     1    P
> 14 14     2    N
> 18 18     3    R
> 15 15     4    O
> 1   1     5    A
> 3   3     6    C
> 9   9     7    I
> 19 19     8    S
> 20 20     9    T
> 10 10    10    J
> 7   7    11    G
> 17 17    12    Q
> 13 13    13    M
> 8   8    14    H
> 11 11    15    K
> 12 12    16    L
> 2   2    17    B
> 6   6    18    F
> 4   4    19    D
> 5   5    20    E
> #rev ... reverses
> > df[rev(ord),]
>    x rsamp Lets
> 5   5    20    E
> 4   4    19    D
> 6   6    18    F
> 2   2    17    B
> 12 12    16    L
> 11 11    15    K
> 8   8    14    H
> 13 13    13    M
> 17 17    12    Q
> 7   7    11    G
> 10 10    10    J
> 20 20     9    T
> 19 19     8    S
> 9   9     7    I
> 3   3     6    C
> 1   1     5    A
> 15 15     4    O
> 18 18     3    R
> 14 14     2    N
> 16 16     1    P
> # successive applications of [ , ][ , ] can be very powerful
> # this is the first 10 of the reverse sorted by rsamp df
            ... er,   ^5^
>
> > df[rev(ord),][1:5,]
>    x rsamp Lets
> 5   5    20    E
> 4   4    19    D
> 6   6    18    F
> 2   2    17    B
> 12 12    16    L
> >
>
> And next time, ... please use dput( ) for offering a sample dataframe.
>
> -- 
> David Winsemius
>
>
> On Mar 5, 2009, at 9:57 PM, Bob Roberts wrote:
>
>> Hi,
>>  I have a data frame and I want to extract the entire rows that  
>> have the 20 largest numbers in column Z. How would I go about doing  
>> that? Thanks.
>>
>>
>>
>>
>> 	[[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.