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]]
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$rsamp)
# creates a sorted vector of row numbers
> df[ord,]
x rsamp Lets
16 16 1 P
14 14 2 N
18 18 3 R
15 15 4 O
1 1 5 A
3 3 6 C
9 9 7 I
19 19 8 S
20 20 9 T
10 10 10 J
7 7 11 G
17 17 12 Q
13 13 13 M
8 8 14 H
11 11 15 K
12 12 16 L
2 2 17 B
6 6 18 F
4 4 19 D
5 5 20 E
#rev ... reverses
> df[rev(ord),]
x rsamp Lets
5 5 20 E
4 4 19 D
6 6 18 F
2 2 17 B
12 12 16 L
11 11 15 K
8 8 14 H
13 13 13 M
17 17 12 Q
7 7 11 G
10 10 10 J
20 20 9 T
19 19 8 S
9 9 7 I
3 3 6 C
1 1 5 A
15 15 4 O
18 18 3 R
14 14 2 N
16 16 1 P
# successive applications of [ , ][ , ] can be very powerful
# this is the first 10 of the reverse sorted by rsamp df
> df[rev(ord),][1:5,]
x rsamp Lets
5 5 20 E
4 4 19 D
6 6 18 F
2 2 17 B
12 12 16 L
>
And next time, ... please use dput( ) for offering a sample dataframe.
--
David Winsemius
On Mar 5, 2009, at 9:57 PM, Bob Roberts wrote:
> Hi,
> I have a data frame and I want to extract the entire rows that
> have the 20 largest numbers in column Z. How would I go about doing
> that? Thanks.
>
>
>
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
On Mar 5, 2009, at 10:38 PM, David Winsemius wrote:> See if this gets you further along: > > ?order > ?rev > ?"[" > > > df <- data.frame(x = 1:20, rsamp = sample(1:20,20), Lets > =LETTERS[1:20]) > > ord <- order(df$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.
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