Recently, in version R2022b they announced the introduction of dictionaries.

I was under the impression that dictionaries were already available, provided by containers.Map. Are dictionaries just a different name mapped to containers.Map? Or are there other differences? I was unable to find anything comparing them online.

CodePudding user response：

From what I can gather, after reading this blog post and the comments under it, and the documentation (I haven’t yet had a chance to experiment with them, so feel free to correct me if I’m wrong):

1. dictionary is an actual primitive type, like double, cell or struct. containers.Map is a “custom class”, even if nowadays the code is built-in, the functionality can never be as integrated as for a primitive type. Consequently, dictionary is significantly faster.
2. dictionary uses normal value semantics. If you make a copy you have two independent dictionaries (note MATLAB’s lazy copy mechanism). containers.Map is a handle class, meaning that all copies point to the same data, modifying one copy modifies them all.
3. containers.Map can use char arrays (the old string format) or numbers as keys (string is implicitly converted to char when used as key). dictionary can use any type, as long as it overloads keyhash. This means you can use your own custom class objects as keys.
4. dictionary is vectorized, you can look up multiple values at once. With a containers.Map you can look up multiple values using the values function, not the normal lookup syntax.
5. dictionary has actual O(1) lookup. If I remember correctly, containers.Map doesn’t.*

^{* No, it is also O(1), at least in R2022b.}