You can't stop people asking the question
Some will just lazily ask without searching at all. Some will search but not find, because no matter how crystal clear you make the title of the original, they will be thinking of the problem in different terms ("matrix operation", "lump data", "interpolate duplicate abscissa values" etc)
You can't stop people answering the question
New users won't know that the question has been asked before. We certainly don't want to discourage new users from answering, so we probably just have to live with this. However it's frustrating to end up with a collection of good answers spread among multiple copies of the same essential question. Perhaps a policy of withholding upvotes subject to moving the answer across might help? "Great answer, but the question is a duplicate. If you delete this answer and repost it here I will gladly upvote it"
Of course the issue of people answering duplicates can be reduced by quickly identifying them as such and getting them closed ASAP, which brings us to the most important point:
Finding duplicates is hard and unrewarding
The issue of rewarding users for finding duplicates has been raised before and presumably dismissed by the SE team as (unless I'm mistaken) there are still no imaginary internet points on offer for finding duplicates. So the problem is how to make it easier to find duplicates. Here's my half-baked suggestion:
A list of "originals" for commonly asked questions, sorted by the
What I mean by that is that while there are usually many many ways to ask a question, there is often one key function that holds the answer. For the question under consideration, the majority of answers use
GatherBy. So the list would have the link to 4332 under
The list would look something like this:
OP is looking for:
- (for plotting y against a function of x) some link
- (to extract values from rules returned by Solve etc) some link
Hopefully you get the idea. I believe a list of commonly duplicated questions ordered like this would make it much easier for experienced users to quickly find the originals.