Restricting one dimension in a stacked bar chart

[annatang]

Hello everyone, 

I am new to the QlikSense and I am now preparing a stacked bar chart to show the number of students in each proficiency level of 8 measurement tests. Since each measurement test has the same proficiency level categories, I create a table which allows the users to browse a particular measurement test and this forms the Stack of dimensions.

Besides, I want to display the chart by Gender or by School, so I add Gender and School into the Bar and Alternative dimensions correspondingly. The chart would be shown as follows:

However, under the Stack dimension, it provides the users to choose the alternative dimension "School", which is not my want. I just want users to select two things, 1) between Gender and School, 2) the name of test, therefore can someone help me to fix this problem? Many thanks!

Sample data 

StudentID | Gender | School | Overall | Analysis | Interpretation | Inference | Eavluation | Explanation | Induction | Deduction

S1 | F | Business | Strong | Weak | Moderate | Strong | Weak | Moderate | Strong | Weak

S2 | M | Science  | Moderate | Moderate | Moderate | Strong | Weak | Moderate | Strong | Weak

S3 | F | Business | Moderate | Weak | Moderate | Strong | Weak | Moderate | Strong | Moderate

S4 | M | Engineering  | Moderate | Moderate | Moderate | Strong | Weak | Moderate | Moderate | Weak

S5 | F | Science  | Weak | Moderate | Moderate | Strong | Weak | Moderate | Strong | Weak

S6 | M | Business | Strong | Strong | Strong | Strong | Weak | Strong | Strong | Moderate