On Sun, Dec 01, 2013 at 09:10:42PM +0530, Reuben wrote: > Hi > > Question 1: > ----------------- > I would like to know the concept of hash map. Additionally, I got to know > that hash maps are equivalent to dictionaries in python. > > I would like to understand the relationship between dictionaries and hash > map better.
Pythin dictionaries are hash maps. A hash map is another name for a hash table. I already answered your earlier question about dictionaries with a description of hash tables: https://mail.python.org/pipermail/tutor/2013-November/098436.html If anything is unclear, please ask. > Question 2: > ------------------ > It is also said that in a list of may be 10,000 elements(specifically > integers), hash maps would be a better option to find the occurrence of > repetitive integers > > How can this be implemented using dictionaries for a list of 10,000 integer > elements? You don't use dicts as lists. If you want a list, use a list: # list of five integers [2, 7, 19, 25, 3] Where hash tables are good is when you want to map a "key" to a "value", or another way to say the same thing, to *associate* a key to a value. Think of a paper dictionary, where every word is followed by a definition -- the key is the word itself, the value is the definition. There are many names for the same thing: dict hash table hash map associative array symbol table mapping For example, if you want to associate (map) a person's name to their birthday: {"Susan": "1985-12-03", "Fred": "1960-03-15", "George": "1973-10-27", } So if you want to map a number to some other piece of data, a dict is must better than a list. Searching a list normally depends on how many items are in the list -- if there are 10,000 items in the list, you will need to inspect 5000 items on average. Searching a dict normally takes exactly the same amount of time whether there is one item or 10000 items. e.g.: {2: "two", 7: "seven", 19: "nineteen", 25: "twenty-five", 3: "three", # and ten thousand more } versus: [(2, "two"), (7, "seven"), (19, "nineteen"), (25: "twenty-five"), (3, "three"), # and ten thousand more ] the dict will be thousands of times faster, on average. -- Steven _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
