[R] Excluding rows from a matrix - best option

[Peter Dalgaard BSA]

José Ernesto Jardim <ernesto at ipimar.pt> writes:

> José Ernesto Jardim wrote:
> 
> > Hi
> >
> > I have a matrix (4 x 950) and I want to remove 3 rows, where the values
> > from the first column are 713, 714 and 715. I can select the rows, one
> > by one, with
> >
> > mat[mat$first==713,]
> > mat[mat$first==714,]
....
> The best way I found after these messages and with your help was
> 
> (i) selecting diferent rows
> 
> mat[(mat$first==c(###, ###, ...)),]
> 
> (ii) excluding diferent rows
> 
> mat[!(mat$first==c(###, ###, ...)),]

Whoa! I don't think that actually works:

> first<-1:6
> first==1:3
[1]  TRUE  TRUE  TRUE FALSE FALSE FALSE
> first==2:4
[1] FALSE FALSE FALSE FALSE FALSE FALSE


You really need the %in% operator:

> first %in% 2:4
[1] FALSE  TRUE  TRUE  TRUE FALSE FALSE

Also, btw: subset(mat, first %in% c(713,714,715)) resp.

subset(mat, !(first %in% c(713,714,715)))
-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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