[R] Reasons to Use R
Right: SAS objects (at least in the base and statistics components of the
system -- there are dozens of add-ons for particular markets) are simple
databases. the predominant model for data manipulation and statistical
calculation is a row by row operation that creates modified rows and/or
accumulates totals. This was pretty much the only way things could be
done in the days when real (and typically virtual) memory was much smaller
than it now is. It can be a pretty efficient model for calculatons that
fit that pattern. One downside of course is that a line of R code can
easily turn into 30 lines of SAS with data steps, sort steps, steps to
accumulate totals, etc.
As noted by a couple of previous writers, S-Plus might be regarded as
somewhat intermediate in its model in that objects constitute files but
rows do not correspond to chunks of adjacent bytes in memory or filespace.
I have thought for a long time that a facility for efficient rowwise
calculations might be a valuable enhancement to S/R. The storage of the
object would be handled by a database and there would have to be an
efficient interface for pulling a row (or small chunk of rows) out of the
database repeatedly; alternatively the operatons could be conducted inside
the database. Basic operations of rowwise calculation and cumulation
(such as forming a column sum or a sum of outer-products) would be
written in an R-like syntax and translated into an efficient set of
operations that work through the database. (Would be happy to share
some jejeune notes on this.) However the main answer to thie problem
in the R world seems to have been Moore's Law. Perhaps somebody could
tell us more about the S-Plus large objects library, or the work that
Doug Bates is doing on efficient calculations with large datasets.
Alan Zaslavsky
[EMAIL PROTECTED]
> Date: Tue, 10 Apr 2007 16:27:50 -0600
> From: "Greg Snow" <[EMAIL PROTECTED]>
> Subject: Re: [R] Reasons to Use R
> To: "Wensui Liu" <[EMAIL PROTECTED]>
>
> I think SAS has the database part built into it. I have heard 2nd hand
> of new statisticians going to work for a company and asking if they have
> SAS, the reply is "Yes we use SAS for our database, does it do
> statistics also?" Also I heard something about SAS is no longer
> considered an acronym, they like having it be just a name and don't want
> the fact that one of the S's used to stand for statistics to scare away
> companies that use it as a database.
>
> Maybe someone more up on SAS can confirm or deny this.
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Re: [R] Reasons to Use R
thanks, I will take a look. __ R-help@stat.math.ethz.ch 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] erratic behavior of match()?
>Is this a consequence of machine error or something else? >Could this be overcome? (It works correctly when integers are used in >the sequences as well as in many other circumstances) The usual solution for testing a==b with floating-point round-off error is abs(a-b) X1=seq(0,1,len=11) > X2=seq(0,1,len=101) > match(X1,X2) [1] 1 11 21 NA 41 51 NA 71 81 91 101 > match(round(X1,2),round(X2,2)) [1] 1 11 21 31 41 51 61 71 81 91 101 In the following case, X2 does not round "exactly" but 7-digit accuracy seems fine. > X2=seq(0,1,len=31) > match(X1,X2) [1] 1 4 7 NA 13 16 NA NA 25 28 31 > match(round(X1,7),round(X2,7)) [1] 1 4 7 10 13 16 19 22 25 28 31 __ R-help@stat.math.ethz.ch 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] random sampling with some limitive conditions?
If I understand your problem, this might be a solution. Assign independent random numbers for row and column and use the corresponding ordering to assign the row and column indices. Thus row and column assignments are independent and the row and column totals are fixed. If cc and rr are respectively the desired row and column totals, with sum(cc)==sum(rr), then n = sum(cc) row.assign = rep(1:length(rr),rr)[order(runif(n))] col.assign = rep(1:length(cc),cc)[order(runif(n))] If you want many such sets of random assignments to be generated at once you can use a few more rep() calls in the expressions to generate multiple sets in the same way. (Do you actually want the assignments or just the tables?) Of course there are many other possible solutions since you have not fully specified the distribution you want. Alan Zaslavsky Harvard U > From: "Zhang Jian" <[EMAIL PROTECTED]> > Subject: [R] random sampling with some limitive conditions? > To: r-help > > I want to gain thousands of random sampling data by randomizing the > presence-absence data. Meantime, one important limition is that the row and > column sums must be fixed. For example, the data "tst" is following: >site1 site2 site3 site4 site5 site6 site7 site8 1 0 0 0 1 1 0 0 0 1 1 1 0 > 1 0 1 1 0 0 0 1 0 1 0 0 0 0 1 0 1 0 1 1 0 1 0 0 0 0 0 0 1 0 1 1 1 1 1 1 0 0 > 0 0 0 0 0 0 0 0 1 0 1 0 1 > > sum(tst[1,]) = 3, sum(tst[,1])=4, and so on. When I randomize the data, the > first row sums must equal to 3, and the first column sums must equal to 4. > The rules need to be applied to each row and column. > How to get the new random sampling data? I have no idea. > Thanks. __ R-help@stat.math.ethz.ch 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.
