I could not find this in Version 4 ACP anymore?

Dropped. I asked before. No reply, so...

ok, so we have to create a plugin...it's too bad, because it was a useful functionality.

This is gone too?!

Wow. I really need this. Why would they remove this?

From what I recall it was removed as it could cause confusion sometimes. I think the solution for the moment is to use flood control though.

This was one of my favorite IPB features.

Yes! Quicker than editing, just reply and... magic. Such a cool feature. Cuts down on the database bulk of more posts than needed as well. Also keeps "post whores" at bay, as they can't reply 6 times in a row for a higher post count.

I know old thread but is there any plugin for that now ?

Open your ACP and type merge in to the search bar, and you will find the setting.

thank you @Nathan Explosion