Good day all

I am using a stacked cross-sectional dataset, called the South African Post-Apartheid Labour Market Series (PALMS), from the years 1993 to 2017.
There is a lot of missing data for the monthly earnings variable. Therefore, I have been requested to figure out how to go about doing a cell mean imputation for item non-response on missing earning figures. This is apparently done by calculating the cell mean of earnings for all those who have the same education (coded to be if they have less than 12 years of schooling, have 12 years or more than 12 years) and belong to the same population group; and then giving those in the same groups with missing earnings this cell mean.

I do not know how to go about doing this. I would understand i could use a loop for the respective years, but I am at a loss with calculating the cell means and imputing them.
Would anyone be able to help?

Regards