Extensions to generate                                     (manual:  [5d] egen)
----------------------

	^egen^ [type] newvar ^=^ fcn^(^stuff^)^ [^if^ exp] [^in^ range] [^,^ options]


Description
-----------

^egen^ creates newvar of the optionally specified storage type equal to 
fcn(stuff).  Depending on fcn(), stuff refers to either an expression or a
varlist, and the options are similarly function dependent.  The functions are:

^tma(^exp^)^ [^, nom^iss ^s^pan^(^#^) not^aper] creates a #-period trailing moving average
        of exp.  The default span is 3; any positive integer is legal.  ^tma()^
        ignores missing values unless there are ^span()^ successive ones.  The
        ^nomiss^ option forces ^tma()^ to return missing values whenever any
        value of exp within the span is missing.  The first ^span()^-1 values
        of newvar are tapered: the first value of newvar is the first value
        of exp; the second value of newvar is the average of the first two
        values of exp; and so on.  The ^notaper^ option sets the first ^span()^-1
        values of newvar to missing.
Description, continued
----------------------

^count(^exp^)^ [^, by(^varlist^)^] creates a constant (within varlist) containing the
	number of nonmissing observations of exp.  Also see ^robs()^ and ^rmiss()^
	below.


^diff(^varlist^)^ creates an indicator variable equal to 1 where the variables in
	varlist are not equal and 0 otherwise.


^group(^varlist^)^ [^, m^issing] returns values 1, 2, ..., for the groups formed by
	varlist.  varlist may contain string, numeric, or both string and nu-
	meric variables.  ^missing^ indicates that missing values in varlist
	(either ^.^ or "") are to be treated like any other number when assigning
	groups instead of missing values be assigned to the group missing.
	(^group()^ is not documented in the manual; see crc27 in STB-12.)


^iqr(^exp^)^ [^, by(^varlist^)^] creates a constant (within varlist) containing the
	interquartile range of exp.  Also see ^pctile()^.


Description, continued
----------------------

^ma(^exp^)^ [^, t(^#^) nom^iss] creates a #-period moving average of exp.  If ^t()^ is
	not specified, ^t(3)^ is assumed.  # must be odd and exp must not pro-
	duce missing values.  Since moving averages are functions of lags and
	leads, ^ma()^ produces missing where the lags and leads do not exist --
	at the beginning and end of the series.  ^nomiss^ forces calculation of
	shorter, uncentered moving averages for the tails.


^max(^exp^)^ [^, by(^varlist^)^] creates a constant (within varlist) containing the
	maximum value of exp.  Also see ^min()^.


^mean(^exp^)^ [^, by(^varlist^)^] creates a constant (within varlist) containing the
	mean of exp.  Also see ^sd()^.


^median(^exp^)^ [^, by(^varlist^)^] creates a constant (within varlist) containing the
	median of exp.  Also see ^pctile()^.



Description, continued
----------------------

^min(^exp^)^ [^, by(^varlist^)^] creates a constant (within varlist) containing the
	minimum value of exp.  Also see ^max()^.


^pctile(^exp^)^ [^, p(^#^) by(^varlist^)^] creates a constant (within varlist) containing
	the #-th percentile of exp.  If ^p()^ is not specified, 50 is assumed,
	meaning medians; also see ^median()^.  # may range from 1 to 99.


^rank(^exp^)^ creates ranks of exp, equal observations are assigned the average
	rank.  This function changes the sort order of your data.


^sd(^exp^)^ [^, by(^varlist^)^] creates a constant (within varlist) containing the
	standard deviation of exp.  Also see ^mean()^.


^std(^exp^)^ [^, m^ean^(^#^) s^td^(^#^)^] creates the standardized values of exp.  Options
	specify the desired mean and standard deviation.  The default is
	^mean(0) std(1)^, producing a mean 0, standard deviation 1 variable.

Description, continued
----------------------

^rsum(^varlist^)^ creates the (row) sum of the variables in varlist, treating
	missing as 0.


^rmean(^varlist^)^ creates the (row) means of the variables in varlist, ignoring
	missing values.  For example, if three variables are specified and,
	in some observations, one of the variables is missing, in those obser-
	vations newvar will contain the mean of the two variables that do
	exist.  Other observations will contain the mean of all three var-
	iables.  Where none of the variables exist, newvar is set to missing.


^robs(^varlist^)^ gives the number of nonmissing variables in varlist for each
	observation (which is the value used by ^rmean()^ for the denominator
	of the mean calculation).


^rmiss(^varlist^)^ gives the number of missing variables in varlist for each
	observation.


Description, concluded
----------------------

^sum(^exp^)^ [^, by(^varlist^)^] creates a constant (within varlist) containing the
	sum of exp.  Also see ^mean()^.



Examples
--------

 . ^egen avg = mean(chol)^
 . ^gen dev = chol - avg^

 . ^egen medgro = median(inc80-inc79)^                (exp, - means subtraction)

 . ^egen avginc = rmean(inc78 inc79 inc80)^
 . ^egen avginc = rmean(inc78 - inc80)^               (varlist, - means through)






Examples, concluded
-------------------

 . ^egen stdscor = std(score)^
 . ^egen stdscore= std(score), mean(100) std(10)^

 . ^egen ttlsales = sum(sales), by(region)^

 . ^egen racesex = group(race sex)
 . ^ir deaths smokes pyears, by(racesex)


Also see
--------

    STB:  dm18 (STB-19); crc27 (STB-12)
 Manual:  [4] functions, [5d] egen
On-line:  ^help^ for ^collapse^, ^functions^, ^generate^