Bin widths are not constant in histogram

[marc ramelet]

Dear StataList,

I have a question regarding bin width in histograms.

I cannot manage to create bins of equal width. It seems that Stata automatically adjusts bin widths, even when I explicitly set the width.

This can be seen in the code below (which uses the classic auto data in case one of you is kind enough to try):

clear all
sysuse auto
summarize price
twoway__histogram_gen price ///
, ///
percent width(300) start(3000) ///
gen (frequency bound)

keep bound frequency
order bound frequency

The "bound" variable is the midpoint of the bins, which is not increasing by a constant increment of 300.

Would you know what I am missing here?

My goal is to export the constant bins and corresponding percents to Excel, which is why I use "twoway histogram".

Many thanks for your consideration, and stay healthy.

Best regards,

Marc

[Arthur Morris]

The bin widths are correct. The command produces a row for all non-empty bins. As you mention, the variable you call 'bound' is the center of the bins, but only non-empty bins. You'll notice the distances between the values of 'bound' are all multiples of your bin width.

[marc ramelet]

Dear Mr Morris,
Thank you very much for your accurate answer!
This is very helpful. I did not think about that.
I now fill in the empty bins by merging the generated non-empty bins to a linear range. That works well.
Thank you for your time!

[marc ramelet]

I write the obtained solution to show the empty bins below, in case this is useful to someone else going forward:

clear all
sysuse auto
summarize price
twoway__histogram_gen price ///
, ///
percent width(500) start(3000) ///
gen (frequency bound)

keep bound frequency
order bound frequency

* Define the bounds as the lower bounds of the bins
replace bound = bound - 250
drop if frequency == .
save hist_temp, replace
clear all

* Create a range with a number of bins of 27 = (16000-3000)/500 + 1
range bound 3000 16000 27

merge m:1 bound using hist_temp
replace frequency = 0 if frequency == .
drop _merge