study view - optimize calculation for Add Chart for Custom Groups
study view - optimize calculation for Add Chart for Custom Groups

Improve code which computes intersection of sample identifier selections
over charts.

Signed-off-by: Abeshouse, Adam A./Sloan Kettering Institute <abeshoua@mskcc.org>

Former-commit-id: 2c5cfda3af6ec885fef41b5ecbc411dffe9dd0eb
alisman/cbioportal-frontend,cBioPortal/cbioportal-frontend,cBioPortal/cbioportal-frontend,cBioPortal/cbioportal-frontend,alisman/cbioportal-frontend,cBioPortal/cbioportal-frontend,alisman/cbioportal-frontend,cBioPortal/cbioportal-frontend,cBioPortal/cbioportal-frontend,alisman/cbioportal-frontend,alisman/cbioportal-frontend,alisman/cbioportal-frontend