R help - Mar 2004 - character -> list

Hi

I have a matrix of type "character" (strangly) and am trying to apply 
the function "aggregate" to it, but unfortunately without success.
It seems to me that aggregate would work, if I only could get rid of the 
quotation marks around each item.

So for a very simple example which looks as my actual data look (of 
course here I put the quotation marks on purpose, but I have no idea 
where they come from in my actual data):

 > x <-
matrix(c("a","b","1","a","c","3","b","b","2"),
nr=3, byrow=T,
dimnames=list(1:3, c("type","group","value")))
 > x
   type group value
1 "a"  "b"   "1"
2 "a"  "c"   "3"
3 "b"  "b"   "2"

I can't access the columns the way I think would be necessary for 
aggregate to work:
 > x$type
NULL

And this seems to be the problem:
 > typeof(x)
[1] "character"

I think I would need to have type "list" to be able to apply
"aggregate".

How can I accomplish this?

Thanks,
David

Use as.data.frame() on the matrix.

HTH,
Andy
> From: David Andel
> 
> Hi
> 
> I have a matrix of type "character" (strangly) and am trying to
apply
> the function "aggregate" to it, but unfortunately without
success.
> It seems to me that aggregate would work, if I only could get 
> rid of the 
> quotation marks around each item.
> 
> So for a very simple example which looks as my actual data look (of 
> course here I put the quotation marks on purpose, but I have no idea 
> where they come from in my actual data):
> 
>  > x <-
matrix(c("a","b","1","a","c","3","b","b","2"),
nr=3, byrow=T,
> dimnames=list(1:3,
c("type","group","value")))
>  > x
>    type group value
> 1 "a"  "b"   "1"
> 2 "a"  "c"   "3"
> 3 "b"  "b"   "2"
> 
> I can't access the columns the way I think would be necessary for 
> aggregate to work:
>  > x$type
> NULL
> 
> And this seems to be the problem:
>  > typeof(x)
> [1] "character"
> 
> I think I would need to have type "list" to be able to apply 
> "aggregate".
> 
> How can I accomplish this?
> 
> Thanks,
> David
> 
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> 
> 

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It would be helpful if you were more explicit on what you mean
by not successful.

Is the problem that:
1. you can't get aggregate to work with character data or 
2. you want to convert the numeric column to numbers or
3. you want to have a structure that has both numbers and character
columns

Also, I am not sure if you actually want the characters or if you
want the character columns converted to factors or, if applicable
to numbers.

In case 1, it actually does work:
> aggregate(x[,-2], list(x[,2]), length)
  Group.1 type value
1       b    2     2
2       c    1     1

In case 2, use as.numeric:
> aggregate(list(value=as.numeric(x[,3])),list(group=x[,2]), mean)
  group value
1     b   1.5
2     c   3.0

In case 3, create a data frame:
x.df <- data.frame(type = I(x[,1]), group = I(x[,2]), value =
as.numeric(x[,3]))

If you want the character columns converted to factors then get
rid of the I's.


Date:   19 Mar 2004 00:47:38 +0100 
From:   David Andel <andel at ifi.unizh.ch>
To:   <R-help at stat.math.ethz.ch> 
Subject:   [R] character - > list 

 
Hi

I have a matrix of type "character" (strangly) and am trying to apply 
the function "aggregate" to it, but unfortunately without success.
It seems to me that aggregate would work, if I only could get rid of the 
quotation marks around each item.

So for a very simple example which looks as my actual data look (of 
course here I put the quotation marks on purpose, but I have no idea 
where they come from in my actual data):
> x <-
matrix(c("a","b","1","a","c","3","b","b","2"),
nr=3, byrow=T,
dimnames=list(1:3,
c("type","group","value")))
> x
type group value
1 "a" "b" "1"
2 "a" "c" "3"
3 "b" "b" "2"

I can't access the columns the way I think would be necessary for 
aggregate to work:
> x$type
NULL

And this seems to be the problem:
> typeof(x)
[1] "character"

I think I would need to have type "list" to be able to apply
"aggregate".

How can I accomplish this?

Thanks,
David