subgroups within graph matrix

[JohnD Wallace]

Hello all,
I'm repeating an old experiment (with new samples), which used a scatter plot matrix to summarized relationships between several characteristics of the samples. The earlier study further binned the samples into 2 categories and displayed them in a single plot using colored markers (blue for category 1, red for category 2). Its straightforward to do this in a regular twoway scatter plot by making if restrictions and using 2 overlaid scatter plots

sysuse auto
graph twoway (scatter weight mpg if foreign==0) (scatter weight mpg if foreign==1)

but when I try this with graph matrix I'm informed it is not a twoway type.

graph twoway (matrix weight mpg displacement if foreign==0)(matrix weight mpg displacement if foreign==1)

Has anyone solved a similar display challenge?

Thank you for your time
John Wallace

[Nick Cox]

Stata is telling you the first problem with your code: matrix is not a twoway type. Fix that and I think you still need a work-around, and here is one:

. sysuse auto, clear 
(1978 Automobile Data)

. gen mymarker = cond(foreign, "+", "o") 

. graph matrix weight mpg displacement, ms(none) mla(mymarker) mlabpos(0)

[JohnD Wallace]

Thank you very much for the work-around, Nick. This accomplishes the end I'm looking for, nicely.
-JW

[Dominik Fluegel]

If you want to have more flexibility in changing the markers, you can use my ado grmatgroups (available on the SSC):

ssc install grmatgroups
sysuse auto, clear

grmatgroups weight mpg displacement, over(foreign) ///
markeroptions(1 msymbol(+) 2 msymbol(Oh))

All best,
Dominik Flügel