What is the difference between a Map and a Dictionary? I am not asking for how they are defined in language X or Y(which seems to be what generally people are asking here on SO), I want to know what is their difference in theory.
I know a Map is an object that maps keys to values. Isn't a Dictionary the same?
Thanks
These are two different terms for the same concept.
Hashtable and HashMap also refer to the same concept.
One is an older term for the other. Typically the term Dictionary was used before the mathematical term Map took hold. Also, Dictionaries tend to have a key type of String, but that's not 100% true everywhere.
Other terms for this concept that are fairly common: associative array and hash.
Typically I assume that a map is backed by a hash table; it connotes an unordered store. Dictionaries connote an ordered store.
There is a tree-based dictionary called a Trie.
In Lisp, it might look like this:
(a (n (d t)) n d )
Which encapsulates the words:
The traversal from the top to the leaf yields a word.
Two terms for the same thing
"Map" is used by Java, C++
"Dictionary" is used by .Net, Python
"Associative array" is used by Javascript, PHP
"Map" is the correct mathematical term, but it is avoided because it has separate meaning in functional programming.
See here.
Yes, they are the same, you may add "Associative Array" to the mix.
using Hashtable or a Hash ofter refers to the implementation.