What is the difference between indexing and hashing?

Answer 1

Hashing is a special form of indexing. Hashing is a way to transform a textual value in a shorter integer value for indexing purpose. This technique is widely used in runtime engine, database, etc.

For example, "This is a test" is hashed as 3325525, a 32-bit integer (I made the value up to demonstrate the use of hashing value).

When the computer need to find "This is a test", it applied the hashing algorithm (there are many ways to do this) to get the integer value of 3325525, and then "looks" up in a table-like structure with that integer value to find the memory location of that string. The look-up from integer to something (a memory location in this case), is called indexing.

Some computer languages do provide indexers in textual way. That is indexing by strings, not just integers. The underlined implementation may have an additional hash look up as:

the key string --- Hased ---> an integer hash value

the storage is storing (integer, ?) ? is an object of some sort

not just (string, ?)

Although the user (the programmer) may simply apply Owner["Windows 7"] directly without knowing "Windows 7" is hashed into 9993939. (Owner is a table may be indexed by strings, or by an integer, like an array)

Please note that even the number 9993939 itself may be hashed into something else, other than the value of 9993939. Owner[9993939] may not have the value as Owner["Window 7"], assume "Windows 7" be hased as 9993939.