[R] Check values in colums matrix

[Berton Gunter]

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
> To: Muhammad Subianto
> 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
> >
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>