[R] Randomly extract rows from a data frame

[David Scott]

On Mon, 19 Feb 2007, Amy Whitehead wrote:

> Hi,
>
> I am looking for a way to randomly extract a specified number of rows from a
> data frame.  I was planning on binding a column of random numbers to the
> data frame and then sorting the data frame using this bound column.  But I
> can't figure out how to use this column to sort the entire data frame so
> that the content of the rows remains together.  Does anyone know how I can
> do this?  Hints for other ways to approach this problem would also be
> appreciated.
>
> Cheers
> Amy
>

It is a bit easier than that.

Here is one way:

> df <- airquality
> rNames <- row.names(df)
> sampRows <- sample(rNames,10)
> sampRows
  [1] "137" "56"  "1"   "135" "62"  "43"  "12"  "128" "86"  "54"
> subset(df,rNames%in%sampRows)
     Ozone Solar.R Wind Temp Month Day
1      41     190  7.4   67     5   1
12     16     256  9.7   69     5  12
43     NA     250  9.2   92     6  12
54     NA      91  4.6   76     6  23
56     NA     135  8.0   75     6  25
62    135     269  4.1   84     7   1
86    108     223  8.0   85     7  25
128    47      95  7.4   87     9   5
135    21     259 15.5   76     9  12
137     9      24 10.9   71     9  14

David Scott
_________________________________________________________________
David Scott	Department of Statistics, Tamaki Campus
 		The University of Auckland, PB 92019
 		Auckland 1142,    NEW ZEALAND
Phone: +64 9 373 7599 ext 86830		Fax: +64 9 373 7000
Email:	d.scott at auckland.ac.nz

Graduate Officer, Department of Statistics