R help - Mar 2009 - Error setting rowname if rowname currently NULL

Hi,

My first post here and new to R so please bear with me (long time programmer
though, helping a friend with some scripts).

I've noticed a behaviour when using rownames() that I think is odd,
wondering if I'm doing something wrong.

To illustrate, say I create a very simple matrix (called fred):

fred<-matrix(,4,2)

It looks like this:

     [,1] [,2]
[1,]   NA   NA
[2,]   NA   NA
[3,]   NA   NA
[4,]   NA   NA

If I now try and set a row name for one of the rows (say the first row) to
"APPLE", by doing this:

rownames(fred)[1] <- "APPLE"

I get an error:

Error in dimnames(x) <- dn : 
  length of 'dimnames' [1] not equal to array extent

However, I found that if I first set all the rownames to anything at all, by
using say:

rownames(fred) <- c(1:4)

Which gives me:

  [,1] [,2]
1   NA   NA
2   NA   NA
3   NA   NA
4   NA   NA

Then my desired command works, and thus:

rownames(fred)[1] <- "APPLE"

Gives me what I want:

      [,1] [,2]
APPLE   NA   NA
2       NA   NA
3       NA   NA
4       NA   NA

So, what this says to me is that to set the row names INDIVIDUALLY, they
first need to be set to something (anything!).

For what I am doing, I need to set the row names one at a time, as I iterate
through a loop. So I found that to do this I first had to set the rownames
to some dummy values as above. Then it works fine. But this seems a little
kludgy and unnecessary to me, and I am wondering what I am doing wrong. Have
just started in R so fumbling my way through somewhat.

Any suggestions would be appreciated, thanks!


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THe problem is that 'rownames(fred)' is NULL and therefore you will
have to define the names of all the rows:
> fred<-matrix(,4,2)
> fred
     [,1] [,2]
[1,]   NA   NA
[2,]   NA   NA
[3,]   NA   NA
[4,]   NA   NA
> rownames(fred)
NULL
> rownames(fred) <- c("Apple",'','','')
> fred
      [,1] [,2]
Apple   NA   NA
        NA   NA
        NA   NA
        NA   NA
>

On Mon, Mar 2, 2009 at 5:58 PM, snubian <stuart.allen at exemail.com.au>
wrote:
>
> Hi,
>
> My first post here and new to R so please bear with me (long time
programmer
> though, helping a friend with some scripts).
>
> I've noticed a behaviour when using rownames() that I think is odd,
> wondering if I'm doing something wrong.
>
> To illustrate, say I create a very simple matrix (called fred):
>
> fred<-matrix(,4,2)
>
> It looks like this:
>
> ? ? [,1] [,2]
> [1,] ? NA ? NA
> [2,] ? NA ? NA
> [3,] ? NA ? NA
> [4,] ? NA ? NA
>
> If I now try and set a row name for one of the rows (say the first row) to
> "APPLE", by doing this:
>
> rownames(fred)[1] <- "APPLE"
>
> I get an error:
>
> Error in dimnames(x) <- dn :
> ?length of 'dimnames' [1] not equal to array extent
>
> However, I found that if I first set all the rownames to anything at all,
by
> using say:
>
> rownames(fred) <- c(1:4)
>
> Which gives me:
>
> ?[,1] [,2]
> 1 ? NA ? NA
> 2 ? NA ? NA
> 3 ? NA ? NA
> 4 ? NA ? NA
>
> Then my desired command works, and thus:
>
> rownames(fred)[1] <- "APPLE"
>
> Gives me what I want:
>
> ? ? ?[,1] [,2]
> APPLE ? NA ? NA
> 2 ? ? ? NA ? NA
> 3 ? ? ? NA ? NA
> 4 ? ? ? NA ? NA
>
> So, what this says to me is that to set the row names INDIVIDUALLY, they
> first need to be set to something (anything!).
>
> For what I am doing, I need to set the row names one at a time, as I
iterate
> through a loop. So I found that to do this I first had to set the rownames
> to some dummy values as above. Then it works fine. But this seems a little
> kludgy and unnecessary to me, and I am wondering what I am doing wrong.
Have
> just started in R so fumbling my way through somewhat.
>
> Any suggestions would be appreciated, thanks!
>
>
> --
> View this message in context:
http://www.nabble.com/Error-setting-rowname-if-rowname-currently-NULL-tp22298797p22298797.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> 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.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

Hi,
At the 1st step, you only assign a name for the 1st row. However, fred has 4
rows which mean you need to assign 4 rownames for these 4 rows.

At the 2nd step, you only "CHANGE" the 1st rowname from 1 to APPLE


If I am wrong please correct me.

Thanks



-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On
Behalf Of snubian
Sent: Monday, March 02, 2009 4:59 PM
To: r-help at r-project.org
Subject: [R] Error setting rowname if rowname currently NULL


Hi,

My first post here and new to R so please bear with me (long time programmer
though, helping a friend with some scripts).

I've noticed a behaviour when using rownames() that I think is odd,
wondering if I'm doing something wrong.

To illustrate, say I create a very simple matrix (called fred):

fred<-matrix(,4,2)

It looks like this:

     [,1] [,2]
[1,]   NA   NA
[2,]   NA   NA
[3,]   NA   NA
[4,]   NA   NA

If I now try and set a row name for one of the rows (say the first row) to
"APPLE", by doing this:

rownames(fred)[1] <- "APPLE"

I get an error:

Error in dimnames(x) <- dn : 
  length of 'dimnames' [1] not equal to array extent

However, I found that if I first set all the rownames to anything at all, by
using say:

rownames(fred) <- c(1:4)

Which gives me:

  [,1] [,2]
1   NA   NA
2   NA   NA
3   NA   NA
4   NA   NA

Then my desired command works, and thus:

rownames(fred)[1] <- "APPLE"

Gives me what I want:

      [,1] [,2]
APPLE   NA   NA
2       NA   NA
3       NA   NA
4       NA   NA

So, what this says to me is that to set the row names INDIVIDUALLY, they
first need to be set to something (anything!).

For what I am doing, I need to set the row names one at a time, as I iterate
through a loop. So I found that to do this I first had to set the rownames
to some dummy values as above. Then it works fine. But this seems a little
kludgy and unnecessary to me, and I am wondering what I am doing wrong. Have
just started in R so fumbling my way through somewhat.

Any suggestions would be appreciated, thanks!


-- 
View this message in context:
http://www.nabble.com/Error-setting-rowname-if-rowname-currently-NULL-tp2229
8797p22298797.html
Sent from the R help mailing list archive at Nabble.com.

______________________________________________
R-help at r-project.org mailing list

PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

snubian wrote:

<snip>
> I've noticed a behaviour when using rownames() that I think is odd,
> wondering if I'm doing something wrong.
>
> To illustrate, say I create a very simple matrix (called fred):
>
> fred<-matrix(,4,2)
>
> It looks like this:
>
>      [,1] [,2]
> [1,]   NA   NA
> [2,]   NA   NA
> [3,]   NA   NA
> [4,]   NA   NA
>   
... and

    rownames(fred)
    # NULL

> If I now try and set a row name for one of the rows (say the first row) to
> "APPLE", by doing this:
>
> rownames(fred)[1] <- "APPLE"
>   
... so now rownames(fred) would have to become a vector of length one,
and you're trying to use a vector of length one to name rows in a matrix
with four rows.  (in principle, you could argue that the vector should
be recycled on such an occassion, as it happens in many other situations.)

hence
> I get an error:
>
> Error in dimnames(x) <- dn : 
>   length of 'dimnames' [1] not equal to array extent
>   
... because 1 != 4

> However, I found that if I first set all the rownames to anything at all,
by
> using say:
>
> rownames(fred) <- c(1:4)
>   
... so that length(rownames(fred)) == 4

> Which gives me:
>
>   [,1] [,2]
> 1   NA   NA
> 2   NA   NA
> 3   NA   NA
> 4   NA   NA
>
> Then my desired command works, and thus:
>
> rownames(fred)[1] <- "APPLE"
>   
... whereby you change one element in rownames(fred) and it still has 4
elements

> Gives me what I want:
>
>       [,1] [,2]
> APPLE   NA   NA
> 2       NA   NA
> 3       NA   NA
> 4       NA   NA
>
> So, what this says to me is that to set the row names INDIVIDUALLY, they
> first need to be set to something (anything!).
>   
not exactly true:

    fred = matrix(, 4, 2)
    rownames(fred)[4] = 'foo'

here you'd set the 4th element of rownames(fred), which fill the first
three with NA, and rownames(fred) has length 4, as needed.

> For what I am doing, I need to set the row names one at a time, as I
iterate
> through a loop. 
is it possible that you don't really need it?

vQ