[R] Best method to add unit information to dataframe ?

[Gabor Grothendieck]

On Mon, Oct 3, 2011 at 10:35 AM, bruno Piguet <bruno.piguet at gmail.com> wrote:
> Dear all,
>
>  I'd like to have a dataframe store information about the units of
> the data it contains.
>
>  You'll find below a minimal exemple of the way I do, so far. I add a
> "units" attribute to the dataframe. But  I dont' like the long syntax
> needed to access to the unit of a given variable (namely, something
> like :
>   var_unit <- attr(my_frame, "units")[[match(var_name, attr(my_frame,
> "names"))]]
>
>  Can anybody point me to a better solution ?
>
> Thanks in advance,
>
> Bruno.
>
>
> # Dataframe creation
> x <- c(1:10)
> y <- c(11:20)
> z <- c(101:110)
> my_frame <- data.frame(x, y, z)
> attr(my_frame, "units") <- c("x_unit", "y_unit")
>
> #
> # later on, using dataframe
> for (var_name in c("x", "y")) {
>   idx <- match(var_name, attr(my_frame, "names"))
>   var_unit <- attr(my_frame, "units")[[idx]]
>   print (paste("max ", var_name, ": ", max(my_frame[[var_name]]), var_unit))
> }

The Hmisc package has some support for this:

library(Hmisc)

DF <- data.frame(x, y, z)
units(DF$x) <- "my x units"
units(DF$y) <- "my y units"

units(DF$x)


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