CSC151 2007S, Class 41: Representing Color Palettes with Vectors

Admin:
* Notes distributed on Assignment 14, including sample solution.
* EC: CS Extra today at 4:30 in 3821 on Scripting Vector Graphics.
* EC: Comedian Kumail Nanjiani '01 at 8:00 Friday in Main.
* EC: Women's Basketball Saturday at 1:30 in the new Darby.
* In this class, Assignment 15 will be optional (for extra credit).

Overview:
* Problems with lists.
* A solution: Vectors.
* Important vector procedures.

Lists: Our favorite way to group data:
* Allow us to group data
* Simple to use: car, cons, cdr and a few more operations

But some problems
* We can't change lists, we make copies with variations
  * Potentially wastes memory
* Finding things deep in the list is expensive (proportional to the
  position in the list)

Designers of Scheme created an alternative to lists: vector
* Like a list: Collects lots of values
* But fast to get to a specified point
* And mutable

So why have lists?
* Sometimes immutable values are good
* TO guarantee fast access, vectors have fixed size; lists are extensible

Operations:
* Creating:
  (vector val1 val2 ... valn) - like list
  (make-vector size value) - make a vector of the specified size, containing
    only one value
  #(val1 val2 ... valn) - DANGEROUS; USE SPARINGLY

* Extract information:
  (vector-ref vec pos)
  (vector-length vec)

* Change information
  (vector-set! vec pos newval)

* COnversion
  list->vector
  vector->list

* Fish : Ghoti