{smcl}
{.-}
help for {cmd:group2hdfe} {right:()}
{.-}
{title:Title}
group2hdfe - Computes the number of restrictions in a linear regression model with two high dimensional fixed effects.
{title:Syntax}
{p 8 15}
{cmd:group2hdfe} {it:{help varname1}} {it:{help varname2}}, [{it:options}]
{p}
{title:Description}
{p} This command calculates the number of restrictions needed to ensure identifiability of the fixed effects
in a linear regression model with two high dimensional fixed effects (2hdfe). The number of restrictions is stored
in r(rest). The command is a Mata implementation of the {help a2group} developed by Amine Ouazad.
{title:Options}
{p 0 4} {cmd:group (}{it:new varname}{cmd:)} Creates a new variable with an indicator for membership
to each connected set.
{p 0 4} {cmd:largest (}{it:new varname}{cmd:)} Creates a new variable with an indicator for membership to the
largest connected dataset.
{p 0 4}{cmdab:verb:ose} Provides more information while the algorithm is running.
{title:Examples}
Example 1:
Compute the number of restrictions in the data and display it.
{p 8 16}{inp:. group2hdfe i j }{p_end}
{p 8 16}{inp:. display r(rest)}{p_end}
Example2:
Identify the largest "connected" data set
{p 8 16}{inp:. group2hdfe i j, largest(big)} {p_end}
{p 8 16}{inp:. keep if big==1} {p_end}
{title:Saved Results}
{cmd:group2hdfe} saves the following in {cmd:r()}:
{synoptset 15 tabbed}{...}
{p2col 5 15 19 2: Scalars}{p_end}
{synopt:{cmd:r(rest)}}number of restrictions (connected sets).{p_end}
{title:Acknowledgment}
This command was based on a previous version of Amine Ouazad's {help a2group} command.
{title:Author}
{p}
Paulo Guimaraes, BPlim, Banco de Portugal, Portugal.
{p}
Email: {browse "mailto:pguimaraes2001@gmail.com":pguimaraes2001@gmail.com}
Comments welcome!
{title:Also see}
{p 0 21}
{help reghdfe} (if installed).
{p_end}