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help for vlc
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Compare value labels across datasets

        vlc [varlist1] [using filename1] [weight] [if exp] [in range]
              [, to(filenamelist) tab pcent nofreq nomiss nozero
              saving(filename2) [replace | append] clear ]

aweights, fweights, iweights and pweights are allowed; see help weights.

Description

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

Options

to(filenamelist) specifies a set of files to which the current file (either in
    memory or specified with 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 quotes.

tab tabulates the frequency of value label assignments in both datasets.

pcent specifies that tabulations of value label assignments should report
    percentages in addition to frequencies.

nofreq suppresses frequencies in tabulations of value label assignments.

nomiss requests that no missing values be tabulated.

nozero suppresses categories with no observations in either dataset.

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.

saving(filename2) specifies a file location to which to write a tab-delimited
    text file of results.

replace specifies that the file specified in saving(filename2) may be
    overwritten if it exists already.

append specifies that the tabulation should be appended to the file specified
    in saving(filename2), assuming it exists already.

Remarks

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

Examples

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

Author

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

Also see

 Manual:  [U] 15.6 Dataset, variable, and value labels,
          [R] label