Better control over multiple axes

[Matthew Lala]

Consider

sysuse auto
twoway (line  length price, yaxis(1) sort) (line  weight price, yaxis(2) sort)  // GRAPH 1
twoway (line  length price, yaxis(2) sort) (line  weight price, yaxis(1) sort)  // GRAPH 2

I find it irritating and counter-intuitive that in both of these graphs, length is on the left Y-axis, even though in the first graph it is specified as yaxis(1) and in the second yaxis(2). This is because the length plot is specified before the weight plot. But I choose the ordering of plots based on which plot I wanted to be underneath the other plot (so it is (partially) covered when the plots overlap). This may conflict with the ordering I want for the axes. Indeed it is quite likely: I normally specify the most "important" plot last, so that it is drawn on top of the other plots, but then if there are multiple Y axes it is associated with the less-prominent right-hand axis rather than the standard left-hand y axis.

Is there a way around this? Or what do people think about asking Stata to make axis placement reflect the axis number, not the plot ordering?

[Andrew Musau]

-yaxis()- is a plot option, and the plots in twoway are defined by the order of plots in the command line. So -yaxis(1)- and -yxis(2)- do not refer to plot 1 and plot 2. They might just as well be -yaxis(5)- and -yaxis(7)-.

help axis_choice_options

Vince Wiggins has a clever workaround here that involves the -alt- suboption of -yscale()-.

sysuse auto, clear
twoway (line  length price, yaxis(2) yscale(alt) sort) ///
(line  weight price, yaxis(1) sort), yscale(alt axis(2))

[Matthew Lala]

Thank you that works great! Andrew Musau as usual to the rescue.

One small clarification is that I was not proposing that -yaxis(1)- and -yxis(2)- should refer to plot 1 and plot 2, but that they should refer to axis locations -- something like odd numbers produce left hand side axes, while even numbers produce right hand side axes.

But anyway, your suggestion works for me. Thank you.