_nobs.hlp

是一个经济学管理应用软件 很难找的 但是经济学学生又必须用到

{smcl}
{* 10mar2005}{...}
{cmd:help _nobs}{right:also see:  {help undocumented}}
{hline}

{title:Title}

{p 4 15 2}
{cmd:_nobs} {hline 2} Programmer's utility for counting the number of
			observations


{title:Syntax}

{p 8 14 2}{cmd:_nobs} {it:varname} [{it:weight}] [{cmd:if} {it:exp}]
		[{cmd:in} {it:range}] [{cmd:,} {cmd:min(}{it:#}{cmd:)}
		{cmdab:zero:weight} ]

{p 4 4 2}
{cmd:fweight}s, {cmd:aweight}s, {cmd:iweight}s, and {cmd:pweight}s are
allowed; see {help weights}.


{title:Description}

{pstd}
{cmd:_nobs} counts the number of observations based on a 0/1 variable giving
the sample.  (Strictly speaking, the variable is evaluated as 0/not 0.)

{pstd}
It is an {hi:rclass} command, and the number of observations are returned
in {hi:r(N)}.

{pstd}
If frequency weights ({cmd:fweight}s) are specified, then the sum of the
weights is used for the number of observations.  If the weights are any other
type, they are marked out, but otherwise ignored.

{pstd}
If the number of observations are less than those specified by the
{cmd:min()} option, an appropriate error message is issued.


{title:Options}

{phang}
{cmd:min(}{it:#}{cmd:)} specifies the minimum allowed number of
observations.  That is, if the number of observations is less than #, an error
message is displayed.  The default is 1.

{phang}
{cmd:zeroweight} specifies that weights of zero are not to be marked
out.


{title:Example}

{pstd}
{cmd:_nobs} is intended for use by programmers.  Its typical use is the
following:

	{cmd:program define myprog}
		{cmd:version} {it:...}
		{cmd:syntax [varlist] [fweight iweight] [if] [in]}
		{cmd:marksample touse}

		{cmd:_nobs `touse' [`weight'`exp'], min(2)}

		{cmd:local N = r(N)}

		{it:...}
	{cmd:end}


{title:Also see}

{psee}
Online:  {helpb count}, {helpb summarize}
{p_end}