[R] rmultinomial() function

[Erik Iverson]

Mary Black wrote:
> After scouring the online R resources and help pages, I still need
> clarification on the function rmultinomial().  I would like to create
> a vector, say of 100 elements, where every element in the vector can
> take on the value of 0, 1 or 2, and where each of those values have a
> specific probability. ie. the probability a given element in the
> vector = 0 is 0.06, 1 = 0.38, 2 = 0.56 (probabilities sum to 1). Can
> I use rmultinomial() function to do this?
> 
> The following code does not seem to produce the result I need, but
> this sort of code is all I could find the R "help" pages:
> 
>> rmultinomial(100,c(0.06,0.38,0.56))
> [1]  3 29 68
>> rmultinomial(100,c(0.06,0.38,0.56),long=TRUE)
> [1] 3 3 2 2 3 2 3 3 2 3 2 3 3 3 2 2 3 3 2 3 1 2 3 3 3 3 3 3 2 3 3 2 3
> 3 3 2 3 2 2 3 2 3 2 3 3 3 2 1 3 3 1 [52] 2 3 2 2 3 3 2 2 2 1 3 3 2 3
> 3 3 3 2 3 3 3 3 2 3 2 3 3 2 3 3 2 3 3 2 3 2 3 3 2 3 3 3 2 3 2 2 2 2 2
> 

You didn't tell us which package has this 'rmultinomial' function.  The 
function 'rmultinom' sounds like it (part of the stats package), but has 
no argument 'long'.

You can just use the 'sample' function to do this.

sample(0:2, 100, prob = c(.06,.38,.56), replace = TRUE)

Best,
Erik Iverson

> 
> Also, I don't really understand the difference between the default
> long=FALSE and long=TRUE.  The R "help" simply states that you use
> "long TRUE to choose one generator, FALSE to choose another one";
> however I could not find any documentation that described what the
> difference between those generators is.  Any clarification would be
> greatly appreciated!
> 
> Thanks,
> 
> Mary
> 
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