Hi and if speed is an issue and object is numeric matrix something like
function(x) which(colSums(abs(diff(x)))==0) is a little bit quicker Cheers Petr On 25 Aug 2006 at 13:39, [EMAIL PROTECTED] wrote: Date sent: Fri, 25 Aug 2006 13:39:48 +1000 From: <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]>, <[EMAIL PROTECTED]>, <[EMAIL PROTECTED]> Copies to: r-help@stat.math.ethz.ch Subject: Re: [R] Check values in colums matrix > As a minor footnote to both of these, I would add that both assume > that all the columns of the dataset are numeric. It doesn't cost much > to generalize it to cover any matrix structure, of any mode: > > constantColmuns <- function(Xmat) > which(apply(Xmat, 2, function(z) length(unique(z)) == 1)) > > > -----Original Message----- > > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Berton Gunter > > Sent: Friday, 25 August 2006 9:37 AM > To: 'Gabor Grothendieck'; > 'Muhammad Subianto' > Cc: r-help@stat.math.ethz.ch > Subject: Re: [R] > Check values in colums matrix > > 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: r-help@stat.math.ethz.ch > > 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 > > ______________________________________________ > 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. Petr Pikal [EMAIL PROTECTED] ______________________________________________ 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.