[R] behaviour of rows and colomns suppression in a matrix

[Olivier ETERRADOSSI]

Thank you, Arun and Sarah

I was not trying to "take row 0 that does not exist", rather  trying "not to 
take" (I wrote "TM[- unused.rows,]") something that does not exist.

So what I understand from Arun's answer is that I was badly using MINUS with 
a vector instead of NOT with a logical.

Olivier

-----Message d'origine-----
De : arun [mailto:smartpink111 at yahoo.com]
Envoyé : jeudi 13 mars 2014 16:13
À : r-help at r-project.org
Cc : Olivier ETERRADOSSI
Objet : Re: [R] behaviour of rows and colomns suppression in a matrix

Hi,
You could use:
 TM2[!margin.Rows <=thresh,!margin.Cols <=thresh] #     [,1] [,2] #[1,]    1 
1 #[2,]    1    1 #[3,]    1    1


#For the first case:
TM1[!margin.Rows <=thresh,!margin.Cols <=thresh] #     [,1] [,2] #[1,]    1 
1 #[2,]    1    1



A.K.





On Thursday, March 13, 2014 10:02 AM, Olivier ETERRADOSSI 
<olivier.eterradossi at mines-ales.fr> wrote:
Hi  List,
while running a script on a set of matrices I came into a case I would not 
have guessed to arrive.
Below is  a small toy example to illustrate the case.
Of course there is a simple workaround (using a simple test), but why does 
this occur, and shouldn’t it be corrected ?

More probably I miss a point, but which one ? Is this behavior obtained on 
purpose and why ?
Sorry if it’s a FAQ… I didn’t find my way to it.
(And sorry for multiple posting if any : I got a warning from r-bounce but 
did not understand it).
Thanks, Olivier


#############################################
# toy example 1 (no problem with this one)

toy.matrix.1<-matrix(c(1,0,1,1,0,1,0,0,0),3,3)
# getting the marginal sums
margin.Rows<- apply(toy.matrix.1,MARGIN=1,FUN=sum)
margin.Cols<- apply(toy.matrix.1,MARGIN=2,FUN=sum)
#giving a threshold for lines and columns suppression
thresh<-0
# finding the items to remove
unused.rows<-which(margin.Rows<=thresh)    # unused.rows == 2
unused.cols<-which(margin.Cols<=thresh)        # unused.cols == 3
TM1<-toy.matrix.1
TM1<-TM1[-unused.rows,]
TM1<-TM1[,-unused.cols]
TM1
#     [,1] [,2]
#[1,]    1    1
#[2,]    1    1                         # OK 
##############################################

# toy example 2 (oops, no rows to suppress…)

toy.matrix.2<-matrix(c(1,1,1,1,1,1,0,0,0),3,3)
# getting the marginal sums
margin.Rows<- apply(toy.matrix.2,MARGIN=1,FUN=sum)
margin.Cols<- apply(toy.matrix.2,MARGIN=2,FUN=sum)
#giving a threshold for lines and columns suppression
thresh<-0
unused.rows<-which(margin.Rows<=thresh)         # unused.rows ==
integer(0)
unused.cols<-which(margin.Cols<=thresh)              # unused.cols == 3
TM2<-toy.matrix.2
TM2<-TM2[-unused.rows,]
TM2<-TM2[,-unused.cols]
TM2
#      [,1] [,2]                    # empty...
###############################################
# I was expecting :
#     [,1] [,2]
#[1,]    1    1
#[2,]    1    1
#[3,]    1    1

# which of course is obtained using :
TM2<-toy.matrix.2
if(length(unused.rows) !=0) {TM2<-TM2[-unused.rows,]}
if(length(unused.rows) !=0 ){TM2<-TM2[,-unused.cols]}
TM2

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.