Dear Manuel, I do understand your point of view, and think that it is reasonable, but in this case, I disagree.
It wouldn't hurt to have an example in ?sample of using a permutation to index a matrix, but this is one of many uses of permutations and it is not possible to show or even to anticipate all of them. To use a programming environment like R effectively, it's necessary to acquire some basic facility with the language (such as an understanding of how indexing works), and it's much more efficient to acquire this facility by reading a manual or book than through help pages. For example, the Introduction to R manual that comes with R has a section on indexing arrays, and most introductory books on R, including free ones, have more detailed explanations of the subject. Regards, John -------------------------------- John Fox Department of Sociology McMaster University Hamilton, Ontario Canada L8S 4M4 905-525-9140x23604 http://socserv.mcmaster.ca/jfox -------------------------------- > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Manuel > López-Ibáñez > Sent: Sunday, April 16, 2006 4:52 AM > To: [email protected] > Subject: Re: [R] permutation of rows of a matrix > > Dear John, > > I understand what you mean. However, when someone is learning > R for the first time or have little experience, such examples > help to understand the connection of different parts of the language. > > Moreover, things that make sense once you know them, can be > difficult to relate in the first place. For example, it would > be interesting to know how many new R users don't know that > there is a manual page for "[". > > I hope you can understand my point of view (you may disagree, though.) > > Regards, > Manuel. > > > John Fox wrote: > > Dear Manuel, > > > > Although ?sample doesn't specifically describe permuting > the rows of a > > matrix, it does say that "sample(x) generates a random > permutation of > > the elements of x (or 1:x)." Indexing the rows of the matrix by a > > permutation of 1:x (where x is the number of rows) doesn't > seem to be much of a leap. > > > > Regards, > > John > > > > -------------------------------- > > John Fox > > Department of Sociology > > McMaster University > > Hamilton, Ontario > > Canada L8S 4M4 > > 905-525-9140x23604 > > http://socserv.mcmaster.ca/jfox > > -------------------------------- > > > > > >>-----Original Message----- > >>From: [EMAIL PROTECTED] > >>[mailto:[EMAIL PROTECTED] On Behalf Of Manuel > >>López-Ibáñez > >>Sent: Saturday, April 15, 2006 9:44 AM > >>To: [email protected] > >>Subject: Re: [R] permutation of rows of a matrix > >> > >>help(sample) does not say anything about randomly permuting > the rows > >>of a matrix M by using M[sample(m,m),]. Perhaps it could be > added as > >>an example of use. > >> > >>John Fox wrote: > >> > >>>Dear Jose, > >>> > >>>M[sample(m, m),] will randomly permute the rows of M. [You > probably > >>>could have figured this out via help.search("permutation"), which > >>>would have led you to sample().] > >>> > >>>Regards, > >>> John > >>> > >>>-------------------------------- > >>>John Fox > >>>Department of Sociology > >>>McMaster University > >>>Hamilton, Ontario > >>>Canada L8S 4M4 > >>>905-525-9140x23604 > >>>http://socserv.mcmaster.ca/jfox > >>>-------------------------------- > >>> > >>> > >>> > >>>>-----Original Message----- > >>>>From: [EMAIL PROTECTED] > >>>>[mailto:[EMAIL PROTECTED] On Behalf Of javargas > >>>>Sent: Saturday, April 15, 2006 7:53 AM > >>>>To: [email protected] > >>>>Subject: [R] permutation of rows of a matrix > >>>> > >>>>How can I generate a random permutation between rows of a > >> > >>matrix M (of > >> > >>>>m rows and n columns)? > >>>> > >>>>Thanks for your help, > >>>> > >>>>Jose > >>>> > >>>>______________________________________________ > >>>>[email protected] mailing list > >>>>https://stat.ethz.ch/mailman/listinfo/r-help > >>>>PLEASE do read the posting guide! > >>>>http://www.R-project.org/posting-guide.html > >>> > >>> > >>>______________________________________________ > >>>[email protected] mailing list > >>>https://stat.ethz.ch/mailman/listinfo/r-help > >>>PLEASE do read the posting guide! > >>>http://www.R-project.org/posting-guide.html > >>> > >> > >> > >>______________________________________________ > >>LLama Gratis a cualquier PC del Mundo. > >>Llamadas a fijos y móviles desde 1 céntimo por minuto. > >>http://es.voice.yahoo.com > >> > >>______________________________________________ > >>[email protected] mailing list > >>https://stat.ethz.ch/mailman/listinfo/r-help > >>PLEASE do read the posting guide! > >>http://www.R-project.org/posting-guide.html > > > > > > > > > > > ______________________________________________ > LLama Gratis a cualquier PC del Mundo. > Llamadas a fijos y móviles desde 1 céntimo por minuto. > http://es.voice.yahoo.com > > ______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! > http://www.R-project.org/posting-guide.html ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
