one of my research colleague resolved the issue.
And I want to share the answer.
To find data out values of no2regrid with respect to New_SDN.
First one need to find out index values of different classes of New_SDN data i.e., 0/ 1 / 2/ 3. and then find those values in no2regrid data. I am writing code below for thye same-
idx= find(New_SDN==0);
NO2SD0=no2regrid(idx);
clear idx
idx= find(New_SDN==1);
NO2SD1=no2regrid(idx);
clear idx
idx= find(New_SDN==2);
NO2SD2=no2regrid(idx);
clear idx
idx= find(New_SDN==3);
NO2SD3=no2regrid(idx);
clear idx
