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help for byhist
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Graph interlaced histograms: for comparing histograms by a categorical variable

    byhist varname [if] [in] [weight] [, by(varname) { frequency |fraction |
            density } name(name_option) tw(twoway_options)]

Description

    byhist makes histograms, with frequencies (optionally fraction/density)
    of one variable optionally shown by categories of another variable.
    fweights, aweights, and pweights are allowed (at user's own risk).

Options 

    by specifies a variable by which to compute histograms. Options after a
        comma within the parentheses are passed to twoway_bar.

    frequency |fraction | density are as in histogram.

    name names the graph something other than "Graph"; see name_option.

    tw(twoway_options) passes options to twoway_bar. Note that options passed
        by default may be superseded in this way, for example y axis labels,
        but some added options may be ignored as a result of existing options
        (e.g. yscale will not override the range specified by the existing y
        axis labels).

    tw?(twoway_options) passes options to twoway_bar. This is a set of
        options tw1(twoway_options), tw2(twoway_options), tw3(
        twoway_options), et cetera, that pass twoway_options to the first set
        of bars, the second set of bars, the third set of bars, and so on.
        See the second example below.

    Other options are passed to twoway__histogram_gen.

Examples

    sysuse auto, clear
    byhist mpg, by(foreign)

    sysuse nlsw88, clear
    byhist wage [fw=hours], by(married) frac
    la var married ""
    byhist wage [fw=hours], by(married) frac
    byhist wage [fw=hours], by(married) frac tw1(color(blue))
        tw2(color(cyan))

Author

    Austin Nichols
    austinnichols@gmail.com

Also see: 

 Manual: [R] graph twoway bar

 Online:  help for histogram, twoway bar; bihist (if installed; install)