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.
