On Mar 30, 2012, at 8:17 AM, inkhorn wrote:
Okay, here's some sample code:
ID = c(1,2,3,"A1",5,6,"A2",8,9,"A3")
fakedata = rnorm(10, 5, .5)
main.df = data.frame(ID,fakedata)
results for my data frame:
main.df
ID fakedata
1 1 5.024332
2 2 4.752943
3 3 5.408618
4 A1 5.362838
5 5 5.158660
6 6 4.658235
7 A2 5.389601
8 8 4.998249
9 9 5.248517
10 A3 4.159490
sample1.df = main.df[sample(nrow(main.df), 4), ]
sample1.df
ID fakedata
5 5 5.158660
9 9 5.248517
4 A1 5.362838
8 8 4.998249
Here's what happens when I put a comma before the variable ID:
sample2.df = main.df[sample(nrow(main.df[! main.df[,"ID"] %in%
sample1.df[,"ID"]]), 5),]
Error in `[.data.frame`(main.df, !main.df[, "ID"] %in% sample1.df[,
"ID"]) :
undefined columns selected
That was not the code I offered, which had no error:
> sample2.df <- main.df[ ! main.df[, "ID"] %in% sample1.df[, "ID"] , ]
> sample2.df
ID fakedata
2 2 5.225752
4 A1 4.788752
5 5 3.973376
6 6 5.565669
8 8 5.369974
9 9 5.954552
If you want to further sub-sample from that complement which I offered
(and that _was_ a random sample from the main dataset albeit not the
particular sample you wanted) , then it is available for further
sampling.
> sample2.df[ sample(nrow(sample2.df), 3), ]
ID fakedata
2 2 5.225752
8 8 5.369974
6 6 5.565669
Here's what happens when I exclude the comma:
sample2.df = main.df[sample(nrow(main.df[! main.df["ID"] %in%
sample1.df["ID"]]), 5),]
You cannot do both steps in one line using that exact strategy. But
you can "chain" uses of "[". You could for instance have constructed
indexes (indices seems to be disappearing from the English languages):
idx <- sample(nrow(main.df), 4)
subset1 <- main.df[ idx, ]
subset2 <- main.df[-idx, ][sample(nrow(main.df)-nrow(subset1), 3), ]
> subset2
ID fakedata
6 6 5.565669
5 5 3.973376
2 2 5.225752
--
David.
sample2.df
ID fakedata
8 8 4.998249
1 1 5.024332
3 3 5.408618
5 5 5.158660
10 A3 4.159490
As you can see, one way I get nothing other than an error, the other
way I
get a sample that doesn't exclude rows that were already included in
the 1st
sample.
Thanks,
Matt Dubins
--
View this message in context:
http://r.789695.n4.nabble.com/Random-sample-from-a-data-frame-where-ID-column-values-don-t-match-the-values-in-an-ID-column-in-a-se-tp4516448p4518878.html
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David Winsemius, MD
West Hartford, CT
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
