On Thu, 1 Mar 2001, BXC (Bendix Carstensen) wrote:
> I have:
>
> > version
> _
> platform i386-pc-mingw32
> arch x86
> os Win32
> system x86, Win32
> status
> major 1
> minor 2.1
> year 2001
> month 01
> day 15
> language R
> > m <- matrix( 1:6, 2, 3 )
> > rownames( m ) <- c( "a", "b" )
> > m
> [,1] [,2] [,3]
> a 1 3 5
> b 2 4 6
> > m[ "a", ]
> [1] 1 3 5
> > m[ "b", ]
> [1] 2 4 6
> > m[ match( "c", rownames(m) ), ]
> [1] NA NA NA
> > m[ "c", ]
> Error: subscript out of bounds
>
> I would have guessed that the last two commands always produced the same
> result.
> Is this a bug or feature? If the latter is the case, what is the use of?
A feature. Look at
> match( "c", rownames(m) )
[1] NA> m[NA, ]
[,1] [,2] [,3]
NA NA NA NA
NA NA NA NA> m[as.numeric(NA), ]
[1] NA NA NA
to see what is going on. Indexing by NA (logical or numeric) can
occasionally be useful.
Most of the time I think you want
> m[ match( "c", rownames(m), nomatch=0 ), ]
> [,1] [,2] [,3]
to omit missing names.
Brian
--
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272860 (secr)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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