Why is my column mean not matching with one calculated via the distribution platform, after excluding row(s)?

[#1]

Calculating column mean before and after excluding a row is giving me same values via JSL. It is different as expected when obtained from the distribution platform. Where am I going wrong in JSL?

Names Default To Here( 1 );
Clear Log();
dt = Open( "$sample_data\Semiconductor Capability.jmp" ); // get data table
//get spec limits into column properties 
obj = dt << Manage Spec Limits( Y( dt << Get Column Group( "Processes" ) ), Show Limits All,  Save to Column Properties(1) ); 
obj << close window;  // close Manage Spec Limits window
colName  =  "M1_M1"; // choose column
colMean = Col Mean(dt:colName); show (colMean); // get column mean
colMin  = Col Minimum(dt:colName); show (colMin); // get column minimum value
//plot distribution
Distribution(Stack(1), Continuous Distribution(Column(:M1_M1 ), Horizontal Layout(1),Vertical(0), Process Capability(0)));
dt << select where( dt:colName == colMin)<< Hide and Exclude; // hide and exclude the minimim value of the column
colMeanNew  = Col Mean(dt:colName); show (colMeanNew); // get column mean again
//plot distribution again
Distribution(Stack(1), Continuous Distribution(Column(:M1_M1 ), Horizontal Layout(1),Vertical(0), Process Capability(0)));

[#2 · Accepted solution]

Col Mean() does not honor the Excluded rows like the JMP Platforms do.  If you use:

colMeanNew = Col Mean( If( Excluded( Row State( Row() ) ), ., dt:colName ) );

it will give you the result you want.

[#3 · Accepted solution]

Col Functions and Row States is a good read regarding this. If you don't mind that the excluded rows will  be treated as their own group, you can also use

Col Mean(dt:colName, Excluded())

When using Col functions in this manner in your script (not in formula) and you have multiple groups (Excluded will have its own group), you have to be a bit careful. You can either modify the current row to be non-excluded onw (Row() = something) or create a formula with the Col function.

Other option would be to use Summarize()

summarize(dt, my_mean = Mean(dt:colName));

[#4]

Note that column formulas with excluded() are re-evaluated each time the row selection is changed:

Caution: Places where Jmp does something unexpected 

For small data tables, this is fine: for large data tables, this causes a noticeable delay.

This problem will be fixed in Jmp 18.