I want to know how to replace the missing values for other groups (by mdate) with the values of group 1 in case of mk and ex variable which are same for all groups. Each group is identified by the stock_id. The illustrative data example is appended.

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input float(date mdate) byte stock_id float rt byte mk int ex
22281 732 1  .21 20 101
22312 733 1  .23 30 255
22340 734 1  .01 40  62
22371 735 1  .27 50   7
22281 732 2 1.21  .   .
22312 733 2 2.52  .   .
22340 734 2 1.11  .   .
22371 735 2  .78  .   .
22281 732 3 3.55  .   .
22312 733 3  .99  .   .
22340 734 3 1.76  .   .
22371 735 3  .29  .   .
end
format %td date
format %tm mdate