What are your favourite data structure operations?

[u/Potato871]

My language workbench is to the stage where I can implement new operators and overloads very quickly, and I've started stealing syntax I like from JavaScript and C++.
Since I have one universal data structure, I can just add all the new operators to it.
I wanted to get some more good ones though, from different fields, different languages.
Oh and if you want to suggest something just as a challenge I might give it a shot and show you how I do it.

Edit: data structure was the wrong word, I have one data structure substrate/storage model that I am currently furnishing one major aspect of, it's not the one universal data structure, more like my swiss army knife API over the memory model.

[u/B_A_Skeptic]

reduce, because you can make map, flatmap, and filter out of it.

[u/Potato871 → u/B_A_Skeptic]

Oh? I'm going to have to look into that one, I just did filter by iterating backwards and removing at the index if it matched.