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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: -onewayplot- on SSC |

Date |
Sat, 5 Jul 2003 23:45:58 +0100 |

Thanks to Kit Baum, a new -onewayplot- package is now downloadable from SSC. Stata 8 is required. To install, type . ssc inst onewayplot This posting is a little long, but two flags: (1) there is a detail of interest to users of Stata 6 or Stata 7 (2) there is stuff here _not_ in the help file for -onewayplot-, so you would be wrong in guessing that all the substance here would all be in the help file. Oneway plots in Stata 8 ======================= One of the graph types in Stata before version 8 was -graph, oneway-. The main idea is to represent a set of values by marks against a magnitude scale, specifically on a horizontal axis. Such plots didn't make the cut in the production of the new graphics, as a few postings on Statalist have elicited. (They are still available, old-style, from -gr7, oneway-, but that lacks the flexibility of the new graphics, and cannot be integrated with it.) One good reason for that decision is that oneway plots are, at least in their simplest versions, a special case of scatter plots, as is shown by . scatter rep78 mpg and even the vertical stroke or pipe symbol can be emulated, as by . gen pipe = "|" . scatter rep78 mpg, ms(none) mlabel(pipe) mlabpos(0) mlabsize(*1.3) However, some people using Stata 8, including myself, have found that they missed oneway plots. When these are useful, it is often in ways that mimic some of the features of dotplots, for example, as implemented in -dotplot-. In 1999, I wrote a program -onewplot- for Stata 6, which was my variant on -graph, oneway-, and it remains on SSC for any interested users of Stata 6 or Stata 7. Its most notable feature is a -stack- option which allows multiple instances of any value to be represented by vertically stacked symbols, thus resembling a (horizontal) dotplot and also, clearly, a histogram. -onewayplot- is -onewplot- rewritten rather drastically for Stata 8 graphics. The magnitude scale can now be horizontal or vertical. (With -gr7, oneway- the magnitude axis is always horizontal. With -dotplot- the magnitude axis is always vertical.) By default, there is no binning of data, but you can bin the way I most like to do it, by specifying a -width()- so that classes are defined by width * floor(varname/width) With -width(5)- mpg values 10-14 are classed as 10, 15-19 as 15, etc. In -dotplot- you can tune the number of bins with the -ny()- option. -centre- and -center- options are allowed to mimic the -dotplot, center- option. In fact, -dotplot, centre- is also legal, but undocumented. Inevitably, there are some limitations: 1. -gr7, oneway rescale- stretches each set of data marks to extend over the whole horizontal range of the graph. There is no equivalent with -onewayplot- (or indeed -dotplot-), although a wrapper program to do that would not be difficult. 2. -onewayplot- has no options for showing means, means +/- SDs, medians or quartiles, in contrast to -gr7, oneway box- or -dotplot-. I don't particularly like the way that -dotplot- adds markers for these statistics, so I didn't want to emulate that. I do like the box-dot or dot-box plots of Leland Wilkinson (1994) http://www.spss.com/research/wilkinson/Publications/less.pdf and of Christopher Wild and George Seber in "Chance encounters", Wiley 2000, in my opinion the best introductory statistics book on the market. The latter's version is cleaner. I haven't implemented those extra boxes, as yet. Using -plot()- to add your own extras ===================================== Nevertheless there is a not too tricky way of adding your own extras to -onewayplot-. This is not documented in the help file as yet, although in due course it will be. -onewayplot- has a -plot()- option, on which see [G] plot_option or the online help for -plot_option-. An example will show something of the possibilities. sysuse auto egen median = median(mpg) , by(rep78) egen loq = pctile(mpg) , by(rep78) p(25) egen upq = pctile(mpg) , by(rep78) p(75) gen rep78_2 = rep78 - 0.2 onewayplot mpg, by(rep78) stack f(0.5) plot(scatter rep78_2 median || rcap upq loq rep78_2, hor legend(off) xtitle("Mileage (mpg)")) If this looks pretty inscrutable, then there are two ways to scrute it, clearly: 1. Copy the commands into your do-file editor and see what it does, noting that the last command starting -onewayplot- should all be on one command line. 2. In broad terms, onewayplot mpg, by(rep78) stack f(0.5) is a variant on a scatter plot of -rep78- against -mpg-. What we do is superimpose a plot -- in fact two plots -- on top of it using -plot()-. The first plot shows the medians as point symbols scatterplot rep78_2 median where -rep78_2- is just 0.2 below -rep78-. The second plot shows the quartiles: rcap upq loq rep78_2, hor draws a horizontal interval |--------------------------| after which we just need to clean up some of the stuff we don't want with two extra options, -legend(off) xtitle("Mileage (mpg)")- If you are still with me, then you'll see that the same sort of trick can be used to add (e.g.) means and confidence intervals to the oneway plot, except that we will have to do a little work to get the confidence limits into variables: -ci- leaves r(lb) and r(ub) in its wake, so here is one way (!) to do it: egen mean = mean(mpg), by(rep78) gen ub = . gen lb = . qui forval i = 1/5 { ci mpg if rep78 == `i' replace ub = r(ub) if rep78 == `i' replace lb = r(lb) if rep78 == `i' } onewayplot mpg, by(rep78) stack f(0.5) plot(scatter rep78_2 mean || rcap ub lb rep78_2, hor legend(off) xtitle("Mileage (mpg)")) There are yet other possibilities. These examples put the intervals (loq -- median -- upq or lower limit -- mean -- upper limit) just below each group of dots. You might prefer just above. That's the main point: you can customise your own displays. Program name too long? ====================== Just possibly, you like -onewayplot-, but the name is too long for your taste. This problem is no problem: write a wrapper, say program owp version 8 onewayplot `0' end and store this as owp.ado wherever you would store onewayplot.ado. The technicality here is that Stata stores whatever follows a command name in local macro 0: you can pick up all that this contains and pass it along to -onewayplot-. In short, if you type . owp <whatever> it will exactly as if you typed . onewayplot <whatever> Similarly .h onewayplot (that ".h" is literal) would be the entire contents of a help file, say owp.hlp, pointing you to the help for -onewayplot-. There are many variants on this trick. In fact, all user programming in Stata is in a sense just some variant on this trick. Nick n.j.cox@durham.ac.uk * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**st: RE: -onewayplot- on SSC [bug fix, update]***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

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