[R] Check values in colums matrix

Gabor Grothendieck ggrothendieck at gmail.com
Fri Aug 25 02:09:02 CEST 2006

```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 <gunter.berton at gene.com> 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: r-help-bounces at stat.math.ethz.ch
> > [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Gabor
> > Grothendieck
> > Sent: Thursday, August 24, 2006 4:28 PM
> > Cc: r-help at 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 at 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
> > >
> > > ______________________________________________
> > > R-help at stat.math.ethz.ch mailing list
> > > https://stat.ethz.ch/mailman/listinfo/r-help
> > http://www.R-project.org/posting-guide.html
> > > and provide commented, minimal, self-contained, reproducible code.
> > >
> >
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