Force y axis to start at 0 and still use automated labeling - plot

Question

I have a plot whose y min starts well above 0. But I want to include 0 as the min of the y-axis and still have Stata automatically create evenly-spaced y-axis labels.
Here is the baseline:
sysuse auto2, clear
scatter turn displacement
This produces:
This is almost what I want, except that the y range does not start at 0.
Based on this answer by Nick Cox (https://www.statalist.org/forums/forum/general-stata-discussion/general/1598753-force-chart-y-axis-to-start-at-0), I modify the code to be:
scatter turn displacement, yscale(range(0 .)) ylabel(0)
This succeeds in starting the y-axis at 0, but the labeling besides 0 goes away:
I proceed to remove `ylabel(0):
scatter turn displacement, yscale(range(0 .))
This produces the opposite problem - the y-axis labels are the same as in the first plot.
How can I have Stata automatically produce the y-axis labels from 0 to the max? For instance, 0, 10, 20, 30, 40, 50 - importantly, though, I have many plots and need a solution that determines the exact values automatically, without needing me to input the y max, etc. So it would not be me who chooses 10, 20, ..., 50, but Stata.

Answer 1

By coincidence, I have been working on a command in this territory. Here is a reproducible example.
sysuse auto, clear
summarize turn, meanonly
local max = r(max)
nicelabels 0 `max', local(yla)
* shows 0 20 40 60
scatter turn displacement, yla(`yla', ang(h))
nicelabels 0 `max', local(yla) nvals(10)
* shows 0 10 20 30 40 50 60
scatter turn displacement, yla(`yla', ang(h))
where nicelabels is at present this code.
*! 1.0.0 NJC 25 April 2022
program nicelabels
/// fudge() undocumented
version 9
gettoken first 0 : 0, parse(" ,")
capture confirm numeric variable `first'
if _rc == 0 {
// syntax varname(numeric), Local(str) [ nvals(int 5) tight Fudge(real 0) ]
syntax [if] [in] , Local(str) [ nvals(int 5) tight Fudge(real 0) ]
local varlist `first'
marksample touse
quietly count if `touse'
if r(N) == 0 exit 2000
}
else {
// syntax #1 #2 , Local(str) [ nvals(int 5) tight Fudge(real 0) ]
confirm number `first'
gettoken second 0 : 0, parse(" ,")
syntax , Local(str) [ nvals(int 5) tight Fudge(real 0) ]
if _N < 2 {
preserve
quietly set obs 2
}
tempvar varlist touse
gen double `varlist' = cond(_n == 1, `first', `second')
gen byte `touse' = _n <= 2
}
su `varlist' if `touse', meanonly
local min = r(min) - (r(max) - r(min)) * `fudge'/100
local max = r(max) + (r(max) - r(min)) * `fudge'/100
local tight = "`tight'" == "tight"
mata: nicelabels(`min', `max', `nvals', `tight')
di "`results'"
c_local `local' "`results'"
end
mata :
void nicelabels(real min, real max, real nvals, real tight) {
if (min == max) {
st_local("results", min)
exit(0)
}
real range, d, newmin, newmax
colvector nicevals
range = nicenum(max - min, 0)
d = nicenum(range / (nvals - 1), 1)
newmin = tight == 0 ? d * floor(min / d) : d * ceil(min / d)
newmax = tight == 0 ? d * ceil(max / d) : d * floor(max / d)
nvals = 1 + (newmax - newmin) / d
nicevals = newmin :+ (0 :: nvals - 1) :* d
st_local("results", invtokens(strofreal(nicevals')))
}
real nicenum(real x, real round) {
real expt, f, nf
expt = floor(log10(x))
f = x / (10^expt)
if (round) {
if (f < 1.5) nf = 1
else if (f < 3) nf = 2
else if (f < 7) nf = 5
else nf = 10
}
else {
if (f <= 1) nf = 1
else if (f <= 2) nf = 2
else if (f <= 5) nf = 5
else nf = 10
}
return(nf * 10^expt)
}
end
EDIT
If you go
sysuse auto, clear
summarize turn, meanonly
local max = r(max)
scatter turn displacement, yla(0(10)`max', ang(h))
scatter turn displacement, yla(0(20)`max', ang(h))
you get good solutions. Clearly in this case we need to know that 10 or 20 is a step size to use. There would be scope to calculate a good width programmatically using your own recipe.
EDIT 10 May 2022
A revised and documented nicelabels is now downloadable from SSC.