[R] Ordering a matrix (and not losing the rownames)

[arun]

Hi  Ramón,

It is for the column index.
For ex:
tags_totals[order(tags_totals[,1],decreasing=TRUE),1,drop=FALSE] #same as previous solution as there is only one column.  
#               [,1]
#Grupos           23
#Wikis            15
#Glosarios        11
#Bases de datos    7
#Taller            5

order(tags_totals[,1],decreasing=TRUE) #creates the row index

#If you don't specify the column index, it will select all the columns.


 tags_totals[1,1] 
#Wikis 
 #  15 
tags_totals[1,1,drop=FALSE] 
#      [,1]
#Wikis   15

tags_totals[1,,drop=FALSE] 
#      [,1]
#Wikis   15


is.matrix(tags_totals[1,1])
#[1] FALSE
is.matrix(tags_totals[1,1,drop=FALSE])
#[1] TRUE



A.K.


Many thanks Arun, 
This is important for me because I will need to do this operation 
many times. However, there is one thing that intrigues me. Why it is 
necessary to put two commas in a row? 

> tags_totals[order(tags_totals[,1],decreasing=TRUE),,drop=FALSE] 
               [,1] 
Grupos           23 
Wikis            15 
Glosarios        11 
Bases de datos    7 
Taller            5 
> tags_totals[order(tags_totals[,1],decreasing=TRUE),drop=FALSE] 
[1] 23 15 11  7  5 

I've been reading around trrying to undestand it, but I can't see the logic. 

Many thanks 


----- Original Message -----
From: arun <smartpink111 at yahoo.com>
To: R help <r-help at r-project.org>
Cc: 
Sent: Friday, August 30, 2013 9:27 AM
Subject: Re: Ordering a matrix (and not losing the rownames)

Hi Ramón,
May be this helps:
tags_totals<-matrix(c(15,11,23,7,5),ncol=1,dimnames=list(c("Wikis","Glosarios","Grupos","Bases de datos","Taller"),NULL))

tags_totals[order(tags_totals[,1],decreasing=TRUE),,drop=FALSE]
#               [,1]
#Grupos           23
#Wikis            15
#Glosarios        11
#Bases de datos    7
#Taller            5

A.K.



Hello, 

I have a matrix like this: 

> tags_totals 
               [,1] 
Wikis            15 
Glosarios        11 
Grupos           23 
Bases de datos    7 
Taller            5 

And I want to order by the value of the first column. I do this: 

ordered_matrix <- as.matrix(tags_totals[order(tags_totals[,1],decreasing=TRUE)]) 

It orders alright, but I lose the rownames, that I need for the graphics 
> ordered_matrix 
     [,1] 
[1,]   23 
[2,]   15 
[3,]   11 
[4,]    7 
[5,]    5 

> rownames(ordered_matrix) 
NULL 

If I try to do it after converting to a dataframe I get an error that I don't understand: 

> tags_totals_frame <- as.data.frame(tags_totals) 
> tags_totals_frame[,1] 
[1] 15 11 23  7  5 
> ordered_frame <- tags_totals_frame[order(tags_totals_frame[,1],decreasing=TRUE)] 
Error en `[.data.frame`(tags_totals_frame, order(tags_totals_frame[, 1],  : 
  undefined columns selected 

Thanks on any help, 

-- 
================================== 
Ramón Ovelar 
Campus Virtual Birtuala UPV/EHU 
Tel: (34) 94 601 3407 
http://campusvirtual.ehu.es