Allignement of Histogram Bars

[Trevor Andrew]

How can I change the alignment of the bars in a histogram without changing the x variable. The bars are centered with the x label. But I would like to have the x labels at the left corner of each bar. Here is my code:

twoway (histogram cont if cont>=-50 & cont<0  , freq discrete lcolor(black) fcolor(blue)) ///
       (histogram cont if cont>=0   & cont<=50, freq discrete lcolor(black) fcolor(red) ),  ///
xline(0) xlabel(-50(10)50) graphregion(color(white)) xtitle(Continous Measure) ytitle(Number of Observations) legend(off)

[Andrew Musau]

You do not present a data example, but the bin, start and width information can guide you in creating the label.

webuse sp500, clear
histogram volume, bin(5) nodraw

Res.:

 histogram volume, bin(5) nodraw
(bin=5, start=4103, width=3841.06)

Implies:

histogram volume, bin(5) xlab(4103(3841)`=3841*6') scheme(s1mono)

Res.:

[Trevor Andrew]

Andrew Musau it doesn't work on my end what you are suggesting. Maybe because I am using discrete x variable? There is no built in option in histogram to center the bars manually?

[Nick Cox]

What you want is not clear to me, but spikeplot might be closer in spirit here.

[Andrew Musau]

Andrew Musau it doesn't work on my end what you are suggesting. Maybe because I am using discrete x variable? There is no built in option in histogram to center the bars manually?

For most cases, you will not be able to show all the labels if using the -discrete()- option as this will include each observation as a bar (or vertical line). If the bars look like bars, you do not have many observations and there will be some binning going on. Therefore, you have to figure out how Stata is doing the binning and as hinted in #2, the start and width information can guide you on this. If you want anything more specific, the onus is on you to present a data example (see FAQ Advice #12).

[Trevor Andrew]

What you want is not clear to me, but spikeplot might be closer in spirit here.

Nick Cox I am trying to align the x label at the left corner of each discrete histogram bar. Usually the x label is centered. I thought that there is a built in option in the histogram command.

[Nick Cox]

You can put the axis labels wherever you want. You may need to spell out binning correspondingly:

sysuse auto, clear
histogram mpg, width(5) start(10) xla(10(5)40)

[Trevor Andrew]

Nick Cox it does not work with discrete histograms. Here is my data example:

sysuse auto, clear
histogram turn if turn>=35 & turn<=45, freq discrete xlab(35(1)45)

I would like that each x label tic is aligned to the left corner of the corresponding bar. E.g. the 35 tic is aligned to the left corner of the first bar 36 tic is aligned to the left corner of the second bar etc.

[Nick Cox]

I’d say the request is contradictory. Discrete bins with width 1 imply integer values and centred labels. I agree with Stata’s logic and would not try to subvert it.

[Trevor Andrew]

Nick Cox the issue is that you have to create the discrete histogram with left or right aligned labels when you want to show graphically the distribution of observations around a cutoff in a regression discontinuity design with a discrete running variable. I have attached an example picture. Is it possible to do something like this?

[Nick Cox]

I don't have a different answer. A histogram like that in #10 can be produced by code like this. I try to match the example by using bins of width 0.1 and a start that implies origin 0.

clear
set seed 2803
set obs 1000
gen y = rnormal(-1, 0.7)
histogram y, width(0.1) start(-4) freq xla(-4/2) xli(0) bfcolor(none) blcolor(gs4) scheme(s1color)

As before, I don't see any need for discrete as an option. .

Different colours for different subsets are a different issue, new in #10.

[Trevor Andrew]

Nick Cox thanks a lot for your help. However your solution works only if the x variable is continuous. If x is is discrete you get spaces between the bars and if you change the width to account for the spaces, the height of each bar does not reflect the number of observations. So what I did is, I used the option discrete, moved the x labels by 0.5 to the left so that the each label is aligned to the left corner of the corresponding bar and renamed each label to represent the discrete category.