# st: adding lines to multiple histograms - revisited -

 From "MA V" <[email protected]> To [email protected] Subject st: adding lines to multiple histograms - revisited - Date Wed, 24 Jan 2007 19:44:29 +0000

I am drawing multiple histograms in one plot by using the "by" option.
e.g. hist age, by(city)
(note: I have 15 cities)
My question was the following: is it possible to add one vertical line to each individual histogram(note that these lines have different values for different cities, i.e. for different histograms)?

Nick suggested that I superimpose a spike plot to each histogram in order to achieve the desired effect by doing the following:
sysuse auto, clear
*Suppose we want our lines at the positions of the means.
egen mean = mean(mpg), by(rep78)
*A first histogram gives us an idea of how high we want the lines to go.
twoway histogram mpg, by(rep78)
gen max = 0.2
*Then superimpose a spike plot on the histograms.
twoway histogram mpg || spike max mean,
by(rep78, legend(off)) yti(Density) xti(Miles per gallon)

This works fine BUT in my case I am ploting 15 different histograms in the same plot and picking a different "max" for each one of them is not really practical. Also, I'm using the rescaling option for both the X and the Y axes since the histograms have different scales.
I was wondering if there is a way of telling Stata that the height of each of the lines (one for each histogram) should be a function of the histogram itself. For example, can we somehow specify that each spike should be as high as the highest bar in each of the histograms? Note: I am plotting density-based histograms.
MA

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