Scatter plot color by variable - stata

Question

I want to make an scatter plot in Stata with points colored according to a categorical variable.
The only way I've found to do this, is to code colors in layers of a twoway plot.
However, this seems a rather convoluted solution for such a simple operation:
twoway (scatter latitud longitud if nougrups4 ==1, mcolor(black)) ///
(scatter latitud longitud if nougrups4 ==2, mcolor(blue)) ///
(scatter latitud longitud if nougrups4 ==3, mcolor(red)) ///
(scatter latitud longitud if nougrups4 ==4, mcolor(green))
Is there a simpler and automatic way to do this?
In this case, the categorical variable nougrups4 came from a cluster analysis. A general solution would be fine, but also a specific solution to draw clusters.

Answer 1

This is how I would do this by hand:
sysuse auto, clear
separate price, by(rep78)
tw scatter price? mpg
drop price?
Or in one line using Nick Cox's sepscatter command from SSC:
sepscatter price mpg, separate(rep78)
The latter command can also output other type of plots with the recast() option.

Answer 2

There isn't a 'simpler' built-in solution for what you want to do.
However, here's a simple wrapper command, which you can extend to meet your needs:
capture program drop foo
program define foo
syntax varlist(min=1 max=3)
quietly {
tokenize `varlist'
levelsof `3', local(foolevels)
local i = 0
local foocolors red green blue
foreach x of local foolevels {
local ++i
local extra `extra' || scatter `1' `2' if `3' == `x', mcolor("`: word `i' of `foocolors''")
}
twoway `extra'
}
end
And a toy example:
clear
set obs 10
generate A = runiform()
generate B = runiform()
generate C = .
replace C = 1 in 1/3
replace C = 2 in 4/7
replace C = 3 in 8/10
foo A B C