[R] strange matrix behaviour: is there a matrix with one row?

[Dimitris Rizopoulos]

this is documented: check ?"[". You need to specify drop = FALSE, 
i.e.,

is.matrix(y[-c(1,2,3), , drop = FALSE])


Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://www.med.kuleuven.be/biostat/
     http://www.student.kuleuven.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: <ryszard.czerminski at novartis.com>
To: "Gabor Grothendieck" <ggrothendieck at gmail.com>
Cc: "Brian Quinif" <bquinif at gmail.com>; <r-help at stat.math.ethz.ch>; 
<r-help-bounces at stat.math.ethz.ch>
Sent: Friday, April 07, 2006 3:16 PM
Subject: [R] strange matrix behaviour: is there a matrix with one row?


> Consider this:
>
>> y <- matrix(1:8, ncol=2)
>> is.matrix(y[-c(1,2),])
> [1] TRUE
>> is.matrix(y[-c(1,2,3),])
> [1] FALSE
>> is.matrix(y[-c(1,2,3,4),])
> [1] TRUE
>
> It seems like an inconsistent behaviour:
> - with 2 or more rows we have a matrix
> - with 1 row we do not have a matrix and
> - with 0 rows we have a matrix again
>
> I just stumbled on this behaviour, because I had a problem
> with my program in which I have assumed that matrix with
> some rows removed is still a matrix, which seems to be mostly
> true, but it is not true if only one row is left.
>
> Comments? Suggestions?
> How to work around this problem - without to many "if" statements?
>
> Best regards,
> Ryszard
>
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