[R] New to R
Gabor Grothendieck
ggrothendieck at gmail.com
Mon Feb 2 23:54:30 CET 2009
Also you don't need return since it automatically returns the value produced by
the last statement that it executes.
On Mon, Feb 2, 2009 at 3:44 PM, Greg Snow <Greg.Snow at imail.org> wrote:
> It is not transposing (it just looks that way). The first result is a vector which is 1 dimensional, but is neither a row or a column. The printed version of it looks like a row, because that is a more compact representation. If you sample enough points you will see it wrap around and be represented as several rows. If it printed as a single column, then the first values would scroll off the screen with only a moderate number of values.
>
> The replicate function then takes these vectors and combines them into a matrix and just happens to use each vector as a column of the new matrix, this is standard, matrices by default are filled by column, look at the output of as.matrix( sample( 6, 4, replace=TRUE ) ) and you will see your vector converted to a matrix of 1 column. It could have been done the other way, but way back the decision was made to do it this way and there are probably a lot of things that would break if it were changed now, so we get to live with it. A single call to 't' is not too much effort to get what we expect.
>
> So in short, a vector is neither a column or a row, but prints as a row for practical reasons, and is converted to a column by default if made into a matrix.
>
> Hope this helps,
>
>
> --
> Gregory (Greg) L. Snow Ph.D.
> Statistical Data Center
> Intermountain Healthcare
> greg.snow at imail.org
> 801.408.8111
>
>
>> -----Original Message-----
>> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
>> project.org] On Behalf Of Joe Hughes
>> Sent: Monday, February 02, 2009 1:09 PM
>> To: R help
>> Subject: Re: [R] New to R
>>
>> All,
>>
>> Thanks for taking the time to reply. I understand a bit more
>> about R
>> and the R way then I did before. The final function looks like this:
>>
>> #######################################################################
>> #######
>> #
>> # Input:
>> # die_size - 4, 6, 8, 10, 20
>> # number_of_dice - How many dice to roll
>> # number_of_rolls - How many times to roll the dice
>> #
>> # Output:
>> # The array holding the results of the rolls
>> #
>> #######################################################################
>> #######
>> #
>> function(die_size, number_of_dice, number_of_rolls=1)
>> {
>> return(t(replicate(number_of_rolls, sample(die_size,
>> number_of_dice,
>> replace=TRUE))))
>> }
>>
>> Before I take a look at the teaching demos, I have one question left.
>>
>> Here is a sequence of commands and the output
>>
>> > sample(6, 4, replace=TRUE)
>> [1] 3 4 5 4
>> > replicate(7, sample(6, 4, replace=TRUE))
>> [,1] [,2] [,3] [,4] [,5] [,6] [,7]
>> [1,] 3 3 6 4 5 6 6
>> [2,] 4 4 6 5 5 1 6
>> [3,] 5 1 4 5 6 5 6
>> [4,] 4 6 3 1 1 2 2
>>
>> Why does replicate transpose the vector before assigning it to the
>> array? The way I would output it would be this
>>
>> [,1] [,2] [,3] [,4]
>> [1,] 3 4 5 4
>> [2,] 3 4 1 6
>> [3,] 6 6 4 3
>> [4,] 4 5 5 1
>> [5,] 5 5 6 1
>> [6,] 6 1 5 2
>> [7,] 6 6 6 2
>>
>> Thanks,
>> Joe
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-
>> guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
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