[R] xtable does not print out units of a variable

[Jeff Newmiller]

On Wed, 18 Jul 2018, Shawn Way wrote:

> I have a dataframe that contains units using the units package. 
> Unfortunately, I really need the units for reporting.  I'm assuming 
> that's because the data is in a class units and xtable doesn't know what 
> to do with this.

If you want a bug or feature in a CONTRIBUTED PACKAGE, then you need to 
communicate with the maintainer:

maintainer( "xtable" )

Do keep in mind that they almost always volunteer their time, so be 
patient, and consider figuring out what code changes they need to make so 
it will work.

More below.

> The following is a MWE:
>
>    library(xtable)
>    library(units)
>    data <- data.frame(x=c(as_units(12,"ft")))
>    xtable(data)
>
>    % latex table generated in R 3.5.1 by xtable 1.8-2 package
>    % Wed Jul 18 17:31:44 2018
>    \begin{table}[ht]
>    \centering
>    \begin{tabular}{rr}
>      \hline
>     & x \\
>      \hline
>    1 & 12.00 \\
>      \hline
>    \end{tabular}
>    \end{table}
>
> What I'm looking for is the line
>
>    1 & 12.00 \\
>
> to be
>
>    1 & 12.00 $ft$\\
>
> Can someone point me in the correct direction to make this happen? 
> Since units are used extensively in engineering calculations, being able 
> to handle this class would be extremely beneficial to engineers that are 
> using R with knitr to generate engineering documents.
>
> Shawn Way

I do want to emphasize that R focuses on consistency among elements within 
columns, not rows, so putting the units into the body of the table is kind 
of visually redundant in most cases. Consider:

####################
library(xtable)
library(units)
#> udunits system database from /usr/share/xml/udunits
data <- data.frame(x=c(as_units(c(12,13),"ft")))
datax <- xtable(data)
names(datax) <- paste0( names(datax)[1]
                       , " ($"
                       , deparse_unit( datax[[1]] )
                       , "$)"
                       )
datax
#> % latex table generated in R 3.4.4 by xtable 1.8-2 package
#> % Wed Jul 18 19:13:29 2018
#> \begin{table}[ht]
#> \centering
#> \begin{tabular}{rr}
#>   \hline
#>  & x (\$ft\$) \\
#>   \hline
#> 1 & 12.00 \\
#>   2 & 13.00 \\
#>    \hline
#> \end{tabular}
#> \end{table}

#' Created on 2018-07-18 by the [reprex package](http://reprex.tidyverse.org) (v0.2.0).
####################

If you have some kind of summary table with different units on each row, 
then you will probably arrive at that information a single-row, many 
column data frame. I usually transpose this into a three-column data frame 
with a description column, a value column, and a units column. I don't use 
the units package so have never tried to adapt it to that process.

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