Re: [R] Check values in colums matrix

From: <Bill.Venables_at_csiro.au>
Date: Fri 25 Aug 2006 - 13:39:48 EST


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: r-help-bounces@stat.math.ethz.ch
[mailto:r-help-bounces@stat.math.ethz.ch] 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: r-help-bounces@stat.math.ethz.ch
> > [mailto:r-help-bounces@stat.math.ethz.ch] 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 <msubianto@gmail.com> 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



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