R help - Apr 2006 - Randomly selecting one row for each factor level [Broadca st]

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
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list 
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
> 
>

This worked for my example data frame but not when I used it on my 
actual data frame because some of the levels of x have only one element. 
  However, when I replace 'sample' with 'some' (from the car
package),
it works like a charm!

Many thanks to Andy and Gabor for their help!

Kelly

Liaw, Andy wrote:
> 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
>>
>>______________________________________________
>>R-help at stat.math.ethz.ch mailing list 
>>https://stat.ethz.ch/mailman/listinfo/r-help
>>PLEASE do read the posting guide! 
>>http://www.R-project.org/posting-guide.html
>>
>>
> 
> 
> 
>
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