Fair enough although in the case of the example it does not appear to be a problem:
> sd(obj.tr) [1] 0.3535534 0.0000000 0.0000000 0.0000000 2.5495098 0.0000000 0.0000000 [8] 1.5811388 0.0000000 Further, if all entries in the matrix are integers, as in the example, then we know that: > nr <- nrow(obj.tr) > round(nr * (nr-1) * sd(obj.tr)) [1] 20 0 0 0 143 0 0 89 0 is all integer too. On 8/24/06, Berton Gunter <[EMAIL PROTECTED]> wrote: > Absolutely. But do note that if the values in obj are the product of > numerical computations then columns of equal values may turn out to be only > **nearly** equal and so the sd may turn out to be **nearly** 0 and not > exactly 0. This is a standard issue in numerical computation, of course, and > has been commented on in this list at least dozens of times, but it's still > a gotcha for the unwary (so now dozens +1). > > -- Bert Gunter > Genentech Non-Clinical Statistics > South San Francisco, CA > > > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of Gabor > > Grothendieck > > Sent: Thursday, August 24, 2006 4:28 PM > > To: Muhammad Subianto > > Cc: [email protected] > > Subject: Re: [R] Check values in colums matrix > > > > Try sd(obj.tr) which will give a vector of standard > > deviations, one per column. > > A column's entry will be zero if and only if all values in the column > > are the same. > > > > On 8/24/06, Muhammad Subianto <[EMAIL PROTECTED]> wrote: > > > Dear all, > > > I apologize if my question is quite simple. > > > I have a dataset (20 columns & 1000 rows) which > > > some of columns have the same value and the others > > > have different values. > > > Here are some piece of my dataset: > > > obj <- cbind(c(1,1,1,4,0,0,1,4,-1), > > > c(0,1,1,4,1,0,1,4,-1), > > > c(1,1,1,4,2,0,1,4,-1), > > > c(1,1,1,4,3,0,1,4,-1), > > > c(1,1,1,4,6,0,1,5,-1), > > > c(1,1,1,4,6,0,1,6,-1), > > > c(1,1,1,4,6,0,1,7,-1), > > > c(1,1,1,4,6,0,1,8,-1)) > > > obj.tr <- t(obj) > > > obj.tr > > > > obj.tr > > > [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] > > > [1,] 1 1 1 4 0 0 1 4 -1 > > > [2,] 0 1 1 4 1 0 1 4 -1 > > > [3,] 1 1 1 4 2 0 1 4 -1 > > > [4,] 1 1 1 4 3 0 1 4 -1 > > > [5,] 1 1 1 4 6 0 1 5 -1 > > > [6,] 1 1 1 4 6 0 1 6 -1 > > > [7,] 1 1 1 4 6 0 1 7 -1 > > > [8,] 1 1 1 4 6 0 1 8 -1 > > > > > > > > > > How can I do to check columns 2,3,4,6,7 and 9 have > > > the same value, and columns 1,5 and 8 have different values. > > > > > > Best, Muhammad Subianto > > > > > > ______________________________________________ > > > [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 > > > and provide commented, minimal, self-contained, reproducible code. > > > > > > > ______________________________________________ > > [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 > > and provide commented, minimal, self-contained, reproducible code. > > > > ______________________________________________ [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 and provide commented, minimal, self-contained, reproducible code.
