[R] Vector with zeros and ones

[Marc Schwartz]

On Apr 22, 2013, at 6:28 PM, Marc Schwartz <marc_schwartz at me.com> wrote:

> On Apr 22, 2013, at 6:21 PM, Ayyappa <ayyappach at gmail.com> wrote:
> 
>> Dear group,
>> 
>> I want to generate a vector of 10 elements that always has 20% zeroes, but with a random ordering of zeroes and ones. Can you please suggest a function to do that in R? I tried 'sample' function but the 20% zeros was not always guaranteed.
>> 
>> Thanks for your help.
>> 
>> Regards,
>> Ayyappa
> 
> 
> Predefine your source vector with the fixed distribution that you desire:
> 
> Vec <- c(rep(0, 2), rep(1, 8))
> 
>> Vec
> [1] 0 0 1 1 1 1 1 1 1 1
> 
> Then sample() from that vector:
> 
> set.seed(1)
> 
>> sample(Vec)
> [1] 1 1 1 1 0 1 1 1 1 0
> 
>> sample(Vec)
> [1] 1 0 1 1 1 1 1 1 0 1
> 
>> sample(Vec)
> [1] 1 0 1 0 1 1 1 1 1 1
> 
>> sample(Vec)
> [1] 1 1 1 0 1 1 1 0 1 1
> 


BTW, I should have mentioned, if you want to sample() as above repeatedly, use ?replicate:

# Repeat the above sampling 5 times:
set.seed(1)

> replicate(5, sample(Vec))
      [,1] [,2] [,3] [,4] [,5]
 [1,]    1    1    1    1    1
 [2,]    1    0    0    1    1
 [3,]    1    1    1    1    1
 [4,]    1    1    0    0    1
 [5,]    0    1    1    1    1
 [6,]    1    1    1    1    1
 [7,]    1    1    1    1    0
 [8,]    1    1    1    0    0
 [9,]    1    0    1    1    1
[10,]    0    1    1    1    1


Regards,

Marc