R help - Dec 2006 - Error: cannot take a sample larger than the population

Hi,
In Splus7 this statement
xlrmN1 <- sample(c(0,1,2),400 ,prob=c(0.02 ,0.93 ,0.05 ))
worked fine, but in R the interpreter reports that the length of the 
vector to chose c(0,1,2) is shorter than the size of many times I want 
to be selected from the vector c(0,1,2).
Any good reason?
See below the error.

 > xlrmN1 <- sample(c(0,1,2),400 ,prob=c(0.02 ,0.93 ,0.05 ))
Error in sample(length(x), size, replace, prob) :
        cannot take a sample larger than the population
 when 'replace = FALSE'
Execution halted

TIA,

Aldi

--

Aldi Kraja wrote:
> Hi,
> In Splus7 this statement
> xlrmN1 <- sample(c(0,1,2),400 ,prob=c(0.02 ,0.93 ,0.05 ))
> worked fine, but in R the interpreter reports that the length of the 
> vector to chose c(0,1,2) is shorter than the size of many times I want 
> to be selected from the vector c(0,1,2).
> Any good reason?
> See below the error.
> 
>  > xlrmN1 <- sample(c(0,1,2),400 ,prob=c(0.02 ,0.93 ,0.05 ))
> Error in sample(length(x), size, replace, prob) :
>         cannot take a sample larger than the population
>  when 'replace = FALSE'
> Execution halted
  So why not use replace = TRUE ?

xlrmN1 <- sample(c(0,1,2),400 ,prob=c(0.02 ,0.93 ,0.05 ), replace=TRUE)

table(xlrmN1)
xlrmN1
  0   1   2
  5 373  22

prop.table(table(xlrmN1))
xlrmN1
     0      1      2
0.0125 0.9325 0.0550
> TIA,
> 
> Aldi
> 
> --
> 
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Partial Summary and discussion:
====================Thank you to Chao Gai, Chuck Cleland, and Jim Lemon for
their suggestion
to use replace=T in R.
There is a problem though (see below)

In the Splus7, sample is defined as
-------------
sample(x, size = n, replace = F, prob = NULL, n = NULL, ...)  where 
replace=F
In Splus7

xlrmN1 <- sample(c(0,1,2),400 ,prob=c(0.02 ,0.93 ,0.05 ))

and the 

table(xlrmN1)/400
    0    1    2
 0.02 0.93 0.05
show that "sample" is working exactly as expected based on the prob
vector.

When "sample" is used in Splus7 with replacement we see the following 
result:
 > xlrmN1 <- sample(c(0,1,2),400 ,replace=T,prob=c(0.02 ,0.93 ,0.05 ))
 > table(xlrmN1)/400
      0     1      2
 0.0125 0.925 0.0625
which I think is working again as expected.

In the R, sample is defined as
---------

sample(x, size, replace = FALSE, prob = NULL)

So the above statement with replace=F did not work (reported error)
but with replace=T produced,
> table(xlrmN1)/400
xlrmN1
     0      1      2 
0.0200 0.9225 0.0575 

which is not exactly the sample with the probabilities provided (0.02,0.93,0.05)

Now let's return to the concept of replace=F and replace=T.
When I ask "sample" to select a sample of 400 from a vector of 3 with
NO replacement, I would think the following
a). create a very large sample from 0, 1, and 2. b). From this large sample,
based on the prob vector select without replacement.
c). As result I expect the probability of selected sample to be exactly the same
with the prob vector (As in Splus7)

When I ask "sample" to select a sample of 400 from a vector of 3 with
replacement, I would think the following
a). create a very large sample from 0, 1, and 2. b). From this large sample,
based on the prob vector select with replacement,
which means some of the previous selected 0, 1, 2 can be selected again.
c). As result I expect the probability of selected sample to be NOT exactly the
same with the prob vector (As in Splus7 and R).

So there are two conclusions: "sample" in R is not working correct, OR
I am missing some precision as a rounding error to produce

prob=c(0.02 ,0.93 ,0.05 ).
Am I misunderstanding the "sample" function in R?

Any suggestions are appreciated.
TIA,

Aldi

Aldi Kraja wrote:
>Hi,
>In Splus7 this statement
>xlrmN1 <- sample(c(0,1,2),400 ,prob=c(0.02 ,0.93 ,0.05 ))
>worked fine, but in R the interpreter reports that the length of the 
>vector to chose c(0,1,2) is shorter than the size of many times I want 
>to be selected from the vector c(0,1,2).
>Any good reason?
>See below the error.
>
> > xlrmN1 <- sample(c(0,1,2),400 ,prob=c(0.02 ,0.93 ,0.05 ))
>Error in sample(length(x), size, replace, prob) :
>        cannot take a sample larger than the population
> when 'replace = FALSE'
>Execution halted
>
>TIA,
>
>Aldi
>
>--
>
>  
>
--