Counting values and creating balance table with Nvals, _n, _N

[Penelope Smart]

First, could someone explain in an easy way how nvals, _n and _N is used? I would like to count all distinct values of a variable and I have seen some codes online using

by ...: gen nvals=_n=1

However, I have problems to understand what is done here.

Second, I have the following code for creating a balance table:

local fixed v1 v2 v3 v4 v5

local fixed_n: word count `fixed'

forvalues i = 1 / `fixed_n' {
local fixed_name: word `i' of `fixed'
local fixed`i' : var label `fixed_name'}

foreach v of local fixed {    
sum `v' if subset==1 }

*comparison 1
foreach v of local fixed {    
xtreg `v' event_1 if subset==1, fe  vce (cluster xfe) 
outreg2 using Table1A}

*comparison 2
foreach v of local fixed {    
xtreg `v' event_2 if subset==1, fe  vce (cluster xfe) 
outreg2 using Table1B}

Can someone explain what is done above to create the table? I am new to Stata and get confused by these loops and _n, so it would be great if someone could explain it step by step. Also, is there an easier way to get the same table, but with a simpler code? Thanks.

[Nick Cox]

I will leave your question on balance tables to others. outreg2 is from SSC and a popular download but I don't ever use it.

distinct from the Stata Journal does things like this.

. webuse grunfeld, clear

. distinct

--------------------------------
         |     total   distinct
---------+----------------------
 company |       200         10
    year |       200         20
  invest |       200        195
  mvalue |       200        198
  kstock |       200        199
    time |       200         20
--------------------------------

. distinct , sort

--------------------------------
         |     total   distinct
---------+----------------------
 company |       200         10
    time |       200         20
    year |       200         20
  invest |       200        195
  mvalue |       200        198
  kstock |       200        199
--------------------------------

. distinct, sort max(10)

--------------------------------
         |     total   distinct
---------+----------------------
 company |       200         10
--------------------------------

.