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From |
vwiggins@stata.com (Vince Wiggins, StataCorp) |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Multiple plots, by() option and reversed yaxis scales/labels |

Date |
Thu, 14 Oct 2010 17:21:59 -0500 |

David Elliott <dcelliott@gmail.com> is drawing a graph with two Y axes and is having difficulty controlling which side of the graph -- left or right -- where each axis is placed. David gives a nice example, which I am going to further simplify by removing the by() option. The by() has nothing to do with the axis placement that is confounding David. Here is an example that exhibits the problem, . sysuse auto . collapse (mean) mpg trunk, by(length foreign) . twoway bar mpg length, yaxis(2) || line trunk length, yaxis(1) David wants yaxis(1) to be on the left of the graph and yaxis(2) to be on the right of the graph, but -twoway- insists on putting yaxis(2) on the left and yaxis(1) on the right. He also notes that he could achieve this by reversing the order of his two plots, but the the bars then occlude his lines, and who would want that. It might be surprising, but the number assigned to an axis has nothing to do with its placement on the graph. -twoway- places the axes in the order in which it encounters them, with no consideration of their assigned number. "What?," you cry. How authoritarian. But, consider -twoway-'s problem, when it sees -yaxis(2)-, it cannot be sure that it will ever see an -yaxis(1)-. Moreover, -twoway- will let you create more than two Y axes, and, in that case just stacks them up on the left of the graph like cord wood. Not to worry. Although you may not like -twoway-'s rules, you can alter them. If there are any axes that you do not like the position of, just tell -twoway- to move them to the alternate (other) side of the graph using the -yscale(alt)- option. Because David does not like the position of either Y axis, we will need to tell both of them to switch to the other side. . twoway bar mpg length, yaxis(2) || line trunk length, yaxis(1) yscale(alt) yscale(alt axis(2)) We typed just -yscale(alt)- rather than the more explicit, but still valid, -yscale(alt axis(1))- because -axis(1)- is the default whenever we do not specify an axis. To alter the side of axis(2), we had to be explicit about the axis number and type -yscale(alt axis(2))-. These options will also work for the more complicated by() graph that David wants to draw. David also noted that a Y axis placed on the right of a by() graph does not include its axis title. We will look into this problem. Until a fix is made, David can explicitly place that title onto the graph using the -r1title()- suboption of by(). This is exactly how the title on the left axis is handled on by() graphs. Continuing with David's example, the full command is . twoway bar mpg length, yaxis(2) || line trunk length, yaxis(1) yscale(alt) yscale(alt axis(2)) by(foreign, r1title("(mean) mpg")) -- Vince vwiggins@stata.com * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: Multiple plots, by() option and reversed yaxis scales/labels***From:*David Elliott <dcelliott@gmail.com>

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