is subtable part of a package?

[Christopher W. Ryan]

With Sweave, I use the latex() command in the Hmisc R package to produce
LaTeX code from an R object, that then compiles into a table nicely in
LaTeX.  I have a table object in R from which I want to produce a
two-part table.

I'd like the first 5 rows of the following to be part of a table, with
its own subcaption, and then the last 5 lines in a second part of the
same overall table, with its own subcaption.

                              Estimate Std. Error
count_(Intercept)            0.9977251  0.1865826
count_e.lab.catshs          -0.0403362  0.0539010
count_e.lab.catsurveillance  0.0653787  0.0582526
count_daily.prev.smooth     -1.1695954  0.7072595
count_testAge               -0.0034302  0.0082225
zero_(Intercept)            -1.3169734  0.6009005
zero_e.lab.catshs           -1.2867920  0.3643731
zero_e.lab.catsurveillance  -0.0200851  0.1929485
zero_daily.prev.smooth       3.8041955  2.2311660
zero_testAge                -0.0037691  0.0264094



I found this rather old entry on tex.stackexchange

https://tex.stackexchange.com/questions/150353/subtables-using-rhmisc

that I think would do the job, with suitable R code, but I cannot find that

\begin{subtable}{.5\textwidth}

command documented anywhere. Is it part of "base" LaTeX (I'm using
TeXLive 2022 on Windows 10)? Part of a package?

Thanks.

--Chris Ryan