{smcl}
{* 31Jan2008}{...}
{hline}
help for {hi:vlc}
{hline}

{title:Compare value labels across datasets}

{p 8 14}{cmd:vlc} [{it:varlist1}]
[{cmd:using }{it:filename1}] [{it:weight}]
[{cmd:if} {it:exp}] [{cmd:in} {it:range}]
{bind:[{cmd:,} {cmd:to(}{it:filenamelist}{cmd:)}}
{cmd:tab} {cmdab:pc:ent} {cmdab:nofr:eq}
{cmdab:nomi:ss} {cmdab:noz:ero}
{cmd:saving(}{it:filename2}{cmd:)}
[{cmd:replace} | {cmd:append}]
{bind:{cmd:clear} ]}

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

{title:Description}

{p}{cmd:vlc} compares value labels across two datasets, and 
optionally compares the distribution of observations (with the 
{cmd:tab} option).  If no filename is specified with {cmd:using},
the data currently in memory are assumed to be the using data.

{title:Options}

{p 0 4}{cmd:to(}{it:filenamelist}{cmd:)} specifies a set of files
to which the current file (either in memory or 
specified with {cmd:using}) should be compared. 
If no comparison file is specified, the value labels in the 
current file are tabulated with no comparison group.
If multiple files are specified, the list of file names may need
to be enclosed in compound double quotes; see help {help quotes}.

{p 0 4}{cmd:tab} tabulates the frequency of value label 
assignments in both datasets.

{p 0 4}{cmd:pcent} specifies that tabulations of 
value label assignments should report 
percentages in addition to frequencies.

{p 0 4}{cmd:nofreq} suppresses frequencies in 
tabulations of value label assignments.

{p 0 4}{cmd:nomiss} requests that no missing values be tabulated.

{p 0 4}{cmd:nozero} suppresses categories with no observations in either dataset.

{p 0 4}{cmd:clear} replaces the data currently in memory.  Without this option,
data that has changed since the last save will not be lost; instead, an error will result.

{p 0 4}{cmd:saving(}{it:filename2}{cmd:)} specifies a file location to 
which to write a tab-delimited text file of results.

{p 0 4}{cmd:replace} specifies that the file specified in
{cmd:saving(}{it:filename2}{cmd:)} may be overwritten if it exists already.

{p 0 4}{cmd:append} specifies that the tabulation should be appended to the file specified in
{cmd:saving(}{it:filename2}{cmd:)}, assuming it exists already.

{title:Remarks}

{p}When {cmd:vlc} terminates, a dataset is in memory containing labels, values,
and frequencies or percentages if requested. {cmd:vlc}
saves no results in {cmd:r()}.  Type {help preserve} before running
{cmd:vlc} to facilitate returning to data in memory.

{title:Examples}

{synoptset 20 tabbed}{...}
{synoptline}
{p 8 12}{stata "ssc install ddf2dct, replace" : ssc install ddf2dct, replace}{p_end}
{p 8 12}{stata "clear" : clear}{p_end}
{p 8 12}{stata "tempfile do dct s96" : tempfile do dct s96}{p_end}
{p 8 12}{stata "ddf2dct using http://www.nber.org/sipp/1996/sipp96l.ddf, dct(`dct') do(`do')" : ddf2dct using http://www.nber.org/sipp/1996/sipp96l.ddf, dct(`dct') do(`do')}{p_end}
{p 8 12}{stata "run `do'" : run `do'}{p_end}
{p 8 12}{stata "describe t??amt" : describe t??amt}{p_end}
{p 8 12}{stata "notes t50" : notes t50}{p_end}
{p 8 12}{stata "save `s96'" : save `s96'}{p_end}
{p 8 12}{stata "tempfile do dct s01" : tempfile do dct s01}{p_end}
{p 8 12}{stata "ddf2dct using http://www.nber.org/sipp/2001/sipp01w1.ddf, dct(`dct') do(`do')" : ddf2dct using http://www.nber.org/sipp/2001/sipp01w1.ddf, dct(`dct') do(`do')}{p_end}
{p 8 12}{stata "clear" : clear}{p_end}
{p 8 12}{stata "run `do'" : run `do'}{p_end}
{p 8 12}{stata "notes t50" : notes t50}{p_end}
{p 8 12}{stata "tempfile do dct s93" : tempfile do dct s93}{p_end}
{p 8 12}{stata "ddf2dct using http://www.nber.org/sipp/1993/sipp93w1.ddf, dct(`dct') do(`do')" : ddf2dct using http://www.nber.org/sipp/1993/sipp93w1.ddf, dct(`dct') do(`do')}{p_end}
{p 8 12}{stata "clear" : clear}{p_end}
{p 8 12}{stata "run `do'" : run `do'}{p_end}
{p 8 12}{stata "notes higrade" : notes higrade}{p_end}
{p 8 12}{stata "save `s93'" : save `s93'}{p_end}
{p 8 12}{stata "vlc higrade, to(`s96')" : vlc higrade, to(`s96')}{p_end}
{p 8 12}{stata "use `s96', clear" : use `s96', clear}{p_end}
{p 8 12}{stata "vlc eeducate, to(`s93')" : vlc eeducate, to(`s93')}{p_end}
{synoptline}
{p 8 12}{stata "clear" : clear}{p_end}
{p 8 12}{stata "tempfile do dct c89" : tempfile do dct c89}{p_end}
{p 8 12}{stata "ddf2dct using http://www.nber.org/cps/cpsmar89_91.doc, dct(`dct') do(`do') drop(FILLER)": ddf2dct using http://www.nber.org/cps/cpsmar89_91.doc, dct(`dct') do(`do') drop(FILLER)}{p_end}
{p 8 12}{stata "run `do'" : run `do'}{p_end}
{p 8 12}{stata "save `c89'" : save `c89'}{p_end}
{p 8 12}{stata "clear" : clear}{p_end}
{p 8 12}{stata "tempfile do dct c92" : tempfile do dct c92}{p_end}
{p 8 12}{stata "ddf2dct using http://www.nber.org/cps/cpsmar92.ddf, dct(`dct') do(`do') drop(FILLER)": ddf2dct using http://www.nber.org/cps/cpsmar92.ddf, dct(`dct') do(`do') drop(FILLER)}{p_end}
{p 8 12}{stata "run `do'" : run `do'}{p_end}
{p 8 12}{stata "save `c92'" : save `c92'}{p_end}
{p 8 12}{stata `"vlc a_hga, to(`c89')"' : vlc a_hga, to(`c89')}{p_end}
{p 8 12}{stata `"g lab92=trim(substr(label1,1,25))"' : g lab92=trim(substr(label1,1,25)}{p_end}
{p 8 12}{stata `"ren label2 lab91"' : ren label2 lab91}{p_end}
{p 8 12}{stata `"li val lab91 lab92, noo clean"' : li val lab91 lab92, noo clean}{p_end}
{synoptline}

{title:Author}

    Austin Nichols
    Urban Institute
    Washington, DC
    austinnichols@gmail.com

{title:Also see}

{p 1 14}Manual:  {hi: [U] 15.6 Dataset, variable, and value labels,}{p_end}
{p 10 14}{hi:[R] label}
{p 0 19}On-line:  help for {help label}, {help labelbook};
{help uselabel}; {help cf};
{stata "findit ddf2dct":ddf2dct}