[R] permutation/randomization

[Greg Snow]

You can randomize the order (permute) of a single column with something
like:

> x <- cbind( x=1:10, y=101:110, z=201:210 )
> rownames(x) <- letters[1:10]
> new.x <- x
> new.x[,1] <- sample(new.x[,1])
> new.x
   x   y   z
a  8 101 201
b 10 102 202
c  5 103 203
d  9 104 204
e  3 105 205
f  1 106 206
g  7 107 207
h  4 108 208
i  2 109 209
j  6 110 210

You could do that for each of the columns that you want randomized.  A
quick way to do a separate randomization on each column is:

> new.x <- apply(x, 2, sample)
> rownames(new.x) <- letters[1:10]
> new.x
   x   y   z
a  2 101 203
b  3 107 204
c  6 102 205
d  1 104 207
e  4 105 208
f  7 108 201
g 10 110 206
h  8 106 209
i  5 103 210
j  9 109 202
> 

Hope this helps,

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
(801) 408-8111
 
 

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Grant Gillis
> Sent: Wednesday, April 09, 2008 12:08 PM
> To: r-help at r-project.org
> Subject: [R] permutation/randomization
> 
> Hello,
> 
> I have what I suspect might be an easy problem but I am new 
> to R and stumped.  I have a data set that looks something like this
> 
> b<-c(2,3,4,5,6,7,8,9)
> x<-c(2,3,4,5,6,7,8,9)
> y<-c(9,8,7,6,5,4,3,2)
> z<-c(9,8,7,6,1,2,3,4)
> data<-cbind(x,y,z)
> row.names(data)<-c('a','b','c','d','e','f','g','h')
> 
> which gives:
> 
>  x y z
> a 2 9 9
> b 3 8 8
> c 4 7 7
> d 5 6 6
> e 6 5 1
> f 7 4 2
> g 8 3 3
> h 9 2 4
> 
> I would like to randomize data within columns. The closest I 
> have been able to come permutes data within the columns but 
> keeps rows together along with row names(example below).  For 
> some context, eventually I would like use this to generate 
> many data sets and perform calculations on these random data 
> sets (I think I know how to do this but we'll see).  So 
> ideally I would like row names to remain the same (in order a 
> through h) and column data to randomize within columns but 
> independently of the other columns.  Just shuffle the data 
> deck I guess
> 
> 
> > data[permute(1:length(data[,1])),]
>   x y z
> b 3 8 8
> c 4 7 7
> h 9 2 4
> e 6 5 1
> f 7 4 2
> a 2 9 9
> g 8 3 3
> d 5 6 6
> 
> 
> Thanks in advance for the help and also for the good advice 
> earlier this week.
> 
> Cheers
> 
> 	[[alternative HTML version deleted]]
> 
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