[R] Randomly selecting one row for each factor level [Broadca st]

[Liaw, Andy]

The following should work:

> dfr.samp <- dfr[tapply(1:nrow(dfr), dfr$x, sample, 1),]
> dfr.samp
   x  y z
10 a 10 J
2  b  2 B
9  c  9 I

Andy

From: Kelly Hildner
> 
> I don't use R much, and I have been unable to figure out how 
> to get the 
> subset of my data frame that I would like.
> 
> For example, if this were my data frame:
> 
>  > dfr <- data.frame(x=rep(letters[1:3], 4), y=(1:12), 
> z=(LETTERS[1:12]))  > dfr
>     x  y z
> 1  a  1 A
> 2  b  2 B
> 3  c  3 C
> 4  a  4 D
> 5  b  5 E
> 6  c  6 F
> 7  a  7 G
> 8  b  8 H
> 9  c  9 I
> 10 a 10 J
> 11 b 11 K
> 12 c 12 L
> 
> I would like to randomly select one row for each level of the 
> factor x 
> and create a new data frame with the results.  For example, 
> the result 
> might be:
> 
>     x  y z
> 1  a  1 A
> 5  b  5 E
> 6  c  6 F
> 
> Any help would be greatly appreciated!
> 
> Thanks,
> Kelly
> 
> -- 
> K. Kelly Hildner, Ph.D.
> NOAA Fisheries
> Southwest Fisheries Science Center
> 110 Shaffer Rd.
> Santa Cruz, CA 95060
> 
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