Make a variable from and average of selected rows in a column to use later as a reference line.

[#1]

Hello,

I want your help with finding an average of selected row in a column and use it as a reference line in a graph.

I have a data table:

A	12.5
B	13.4
B	17.5
B	12.8
A	11.1
A	19.4
B	13.8

 I want to make a variable that is an average of all the “B” line values ((13.4+17.5+12.8+13.8)/4) in the example above.

Then I am going to use it as a reference line in a Bivariate graph.

[#2]

@ileshem , 
  Once the data table is openend , select random rows . You can do this by : 
Rows > Row Selection > Select Randomly

dt = Open( "$SAMPLE_DATA/Big Class.jmp" );

AgeVals = :age << Get Values ; // Get Values in Age Column 

SR = dt << Get Selected Rows(); // Get Selected Rows 

RequiredVar = AgeVals[SR,0]; // Desired Values subset from Column Values 

[#3]

Thanks for the prompt replay,
I was able to create a new table with the rows I wanted, but I am not sure how to calculate the MEAN of that column (VALUE) into a variable.
my_list = {"B"};
dtsub1 = dtEPData << subset(
rows( dtEPData << get rows where( Contains( my_list, :TYPE ) ) ),
Selected columns only( 0 ));



TYPE VALUE
A 12.5
B 13.4
B 17.5
B 12.8
A 11.1
A 19.4
B 13.8

Dtsub1=
TYPE VALUE
B 13.4
B 17.5
B 12.8
B 13.8

[#4]

@ileshem , 
Col Mean() - if you want to use the column 

Mean() - if you want to use the matrix or a separate variable 

dt = Open( "$SAMPLE_DATA/Big Class.jmp" );

dt << Select Randomly( 0.3 );

dt1 = dt << Subset(Selected Rows( 1 ), selected columns( 0 )); 

Res = Col Mean(dt1:age); 

Show(Res);

[#5 · Accepted solution]

If I am understanding what you want correctly, try creating a new variable using the Col Mean function with your first column as a "By" variable.  Then create another column with an IF statement that uses the B mean value for both groups A and B.  That column will then all have the same value = mean of the group B values.