Add price information based on reference number to different observation

Hi

I have a large dataset that includes some observatios that are identified as either E or A.
Observation A and E have a common reference ID number.
Observation A incudes price information whereas E does not. However based on the reference number I would like to add the price information from observation A to observation E.

So something like if ref # in obs A equals ref # in obs E then add Price from obs A to obs E.

I have tried looking at the merge function, but as far as I can tell that won't work.

Is it a if-else-then function that needs to be applied?

Any help would be much appreciated.

Thanks