[R] How to retrieve a vector of a data.frame's variable attributes?

[David Winsemius]

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