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.s...@imail.org 801.408.8111 > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@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@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@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.
