[R] Coin Toss Simulation
Erik Iverson
eriki at ccbr.umn.edu
Wed Oct 13 20:18:32 CEST 2010
Shiv wrote:
> I am trying a simple toin coss simulation, of say 200 coin tosses. The idea
> is to have a data frame like so:
> Experiment# Number_Of_Heads
> 1 104
> 2 96
> 3 101
>
> So I do:
>
> d <-data.frame(exp_num=c(1,2,3)); /* Just 3 experiments to begin with */
> d$head_ct <-sum(sample(0:1,200,repl=TRUE));
/* */ is not a valid comment in R, and you don't need ';' either :)
Just try evaluating the right hand side so that the R interpreter
prints the result. This is just calling sample once, and therefore
you only get one number, 85 in your case.
> d;
> exp_num head_ct
> 1 1 85
> 2 2 85
> 3 3 85 /* the same scalar value is
> applied to all the rows */
>
> So I tried using "within", and "for", and making the "sum( " as a
> function, and I end up with the same...I get the same constant value. But
> what I want of course is different "samples"....
Look at ?replicate or just use ?rbinom directly
d <-data.frame(exp_num = 1:3)
d$head_ct <- rbinom(nrow(d), 200, prob = 0.5)
>
>
>
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