R help - Apr 2011 - How to retrieve a vector of a data.frame's variable attributes?

Hi,

I have a data.frame with 100 variables and I have assigned a "label",
"units" and "category" attribute to each variable. I would
like to reorder
the variables in the data.frame by the "category" attributes but
can't find
a way.

For example, the first variable is:
> attributes(hh$aez)
$levels
[1] "coastal"  "forest"   "savannah"

$class
[1] "labelled" "factor"  

$label
[1] ecological zone
93 Levels: 10 quantiles of welfare  ... year of the interview

$units
[1] class
24 Levels: '05 PPP USD / year cedis / year cedis /year class geo-1 ... years

$category
[1] geography
7 Levels: agriculture demography design expenditure geography ... welfare

I have tried:

hh <- hh[, order(attr(hh, "category"))]
hh <- hh[, order(attr(hh[, 1:100], "category"))]
hh <- hh[, order(attr(dimnames(hh), "category"))]

but all the right-hand side assignments above return NULL.

Thanks very much for your help with this simple task!

--Mel.



_______________________
 Melanie Bacou
 3110 Wisconsin Ave, NW 
 Washington DC, 20016 
 +1 (202) 492-7978
 mel at mbacou.com

On Apr 17, 2011, at 4:21 PM, Bacou, Melanie wrote:
> Hi,
>
> I have a data.frame with 100 variables and I have assigned a
"label",
> "units" and "category" attribute to each variable. I
would like to
> reorder
> the variables in the data.frame by the "category" attributes but
> can't find
> a way.
>
Something like lapply(hh, attr, which="category") might return  
something potentially useful. You obviously have a test case, but have  
failed to offer it up. Possibly using order() around that might get  
all the like category variables together.

> For example, the first variable is:
>
>> attributes(hh$aez)
> $levels
> [1] "coastal"  "forest"   "savannah"
>
> $class
> [1] "labelled" "factor"
>
> $label
> [1] ecological zone
> 93 Levels: 10 quantiles of welfare  ... year of the interview
>
> $units
> [1] class
> 24 Levels: '05 PPP USD / year cedis / year cedis /year class  
> geo-1 ... years
>
> $category
> [1] geography
> 7 Levels: agriculture demography design expenditure geography ...  
> welfare
>
> I have tried:
>
> hh <- hh[, order(attr(hh, "category")) ]
Did you look at what order(attr(hh, "category")) returns. Since you  
assigned the attribute to individual columns (which are arranged as a  
list, you cannot expect the whole object to return anything useable  
when queried with attr().
> hh <- hh[, order(attr(hh[, 1:100], "category"))]
(It would be the same since hh == hh[,1:100] )

> hh <- hh[, order(attr(dimnames(hh), "category"))]
dimnames would _not_ have any attributes. And attr can only work on  
one object at a a time anyway,
>
> but all the right-hand side assignments above return NULL.
>
> Thanks very much for your help with this simple task!
>
> --Mel.
>
>
>
> _______________________
> Melanie Bacou

David Winsemius, MD
West Hartford, CT