[R] Binomial

[(Ted Harding)]

On 12-May-11 09:02:45, Alexander Engelhardt wrote:
> Am 12.05.2011 10:46, schrieb blutack:
>> Hi, I need to create a function which generates a Binomial random
>> number
>> without using the rbinom function. Do I need to use the choose
>> function or
>> am I better just using a sample?
>> Thanks.
> 
> I think I remember other software who generates binomial data
> with e.g. pi=0.7 by
> 
> pi <- 0.7
> x <- runif(100)>pi
> summary(x)
> 
>   -- Alex

That needs to be the other way round (and perhaps also convert
it to 0/1):

  x <- 1*(runif(100) < pi)

since Prob(runif > pi) = (1 - pi).

Comparison:

  pi <- 0.7
  x <- runif(100)>pi
  x[1:10]
  #  [1] FALSE  TRUE  TRUE FALSE FALSE  TRUE  TRUE  TRUE FALSE FALSE
  sum(x)/100
  # [1] 0.36

  x <- 1*(runif(100) < pi)
  x[1:10]
  # [1] 0 0 1 1 1 1 1 0 1 0
  sum(x)/100
  # [1] 0.62

Ted

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Date: 12-May-11                                       Time: 10:21:26
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