Hi my data's dummy 'chaebol' has its value only when year = 2004.
How can I replace the value of 1996 by the same value as 2004 for each firmid?

thank you.

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input str6 firmid float year double asset byte chaebol
"000020" 1996   28259495 .
"000020" 2004   48186088 0
"000070" 1996  421634354 .
"000070" 2004  374350110 1
"000100" 2004  205853387 0
"000100" 1996  144924321 .
"000140" 2004 1290148390 1
"000140" 1996  983906135 .
"000220" 2004   29482372 0
"000220" 1996    6159711 .
"000230" 2004   74269529 0
"000230" 1996   27699544 .
"000320" 2004  146142011 0
"000320" 1996   70410218 .
"000430" 2004  142973946 0
"000430" 1996  106637687 .
"000480" 1996   87579814 .
"000480" 2004   68576928 0
"000490" 2004  121681902 0
"000490" 1996   88517309 .
"000500" 1996   60492603 .
"000500" 2004   92325546 1
"000520" 1996    6364544 .
"000520" 2004   17982517 0
"000590" 2004   35330184 0
"000590" 1996   14533334 .
"000640" 1996   46398066 .
"000640" 2004  186631617 0
"000650" 1996   17102946 .
"000650" 2004   22448651 0
"000670" 2004  404231338 1
"000670" 1996  109286087 .
"000700" 2004 3292007620 1
"000700" 1996 1852004833 .
"000880" 1996  543269083 .
"000880" 2004  779888412 1
"000890" 1996   63453223 .
"000890" 2004   90026913 0
"000970" 2004   93380640 0
"000970" 1996   12573848 .
"000990" 2004  459114340 1
"000990" 1996   66795516 .
"001040" 1996  880766514 .
"001040" 2004  969657971 1
"001060" 2004   93182953 0
"001060" 1996   35565684 .
"001080" 1996   29543083 .
"001080" 2004   96897684 0
"001120" 1996  175916675 .
"001120" 2004  193549685 1
"001130" 2004  114773996 0
"001130" 1996   30945961 .
"001140" 2004   25879110 0
"001140" 1996   12975089 .
"001210" 1996   89901905 .
"001210" 2004  119539694 0
"001230" 2004 1584426731 1
"001230" 1996  583272157 .
"001340" 2004   59340413 0
"001340" 1996   35424128 .
"001460" 1996   75982454 .
"001460" 2004  147393982 0
"001470" 2004  214133707 0
"001470" 1996   72399099 .
"001530" 2004   88432872 0
"001530" 1996  183814351 .
"001620" 1996   21019573 .
"001620" 2004   42860335 0
"001680" 2004  550244868 0
"001680" 1996   93694966 .
"001740" 1996   87533066 .
"001740" 2004 1770056619 1
"001790" 2004  167809085 0
"001790" 1996   86010122 .
"001820" 1996   14528497 .
"001820" 2004   15355972 0
"001880" 1996   23523798 .
"001880" 2004    7195062 1
"002020" 2004 1003823716 1
"002020" 1996  729338774 .
"002030" 1996  152737683 .
"002030" 2004  288216881 0
"002070" 1996   17822714 .
"002070" 2004   63450207 0
"002210" 2004   28858778 0
"002210" 1996   23202529 .
"002240" 1996   45849936 .
"002240" 2004  117037787 0
"002380" 1996  343722055 .
"002380" 2004 1179028364 1
"002390" 2004   92473723 0
"002390" 1996   91011028 .
"002420" 1996    3607471 .
"002420" 2004   20439394 0
"002620" 2004   46438962 0
"002620" 1996   11734839 .
"002720" 1996   13431501 .
"002720" 2004   30693353 0
"002760" 2004   10444979 0
"002760" 1996    8135527 .
end