R help - Oct 2010 - Coin Toss Simulation

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));
 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"....



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try this:

n <- 3
data.frame(Exp = seq_len(n),
     Heads = rbinom(n, 200, 0.5))


I hope it helps.

Best,
Dimitris


On 10/13/2010 7:28 PM, 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));
>   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"....
>
>
>
-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
Fax: +31/(0)10/7043014
Web: http://www.erasmusmc.nl/biostatistiek/

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)


> 
> 
>