Ring/Lessons/Lists

Lists

In this chapter we are going to learn how to deal with lists.

Create Lists

We can create new lists by defining the list items inside square bracts.

Example:

	aList = [1,2,3,4,5]

Also we can create new lists using the : operator

Example:

	aList = 1:5
	aList2 = "a":"z"

Also we can create lists using the list() function

Syntax:

	list = list(size)

Example

	aList = list(10)	# aList contains 10 items

.. note:: the list index start from 1

Add Items

To add new items to the list, we can use the Add() function.

Syntax:

	Add(List,Item)

Example:

	aList = ["one","two"]
	add(aList,"three")

Also we can do that using the + operator.

Syntax:

	List + item

Example:

	aList = 1:10	# create list contains numbers from 1 to 10
	aList + 11	# add number 11 to the list
	see aList	# print the list

Get List Size

We can get the list size using the len() function

Syntax:

	Len(List)

Example:

	aList = 1:20  see len(aList)  # print 20

Delete Item From List

To delete an item from the list, we can use the del() function

Syntax:

	del(list,index)

Example:

	aList = ["one","two","other","three"]
	Del(aList,3)	# delete item number three
	see aList   	# print one two three

Get List Item

To get an item from the list, we uses the next syntax

	List[Index]

Example:

	aList = ["Cairo","Riyadh"]
	see "Egypt : " + aList[1] + nl +
	    "KSA   : " + aList[2] + nl

Set List Item

To set the value of an item inside the list, we can use the next syntax

	List[Index] = Expression

Example:

	aList = list(3)	# create list contains three items
	aList[1] = "one" aList[2] = "two" aList[3] = "three"
	see aList

Search

To find an item inside the list we can use the find() function

Syntax:

	Find(List,ItemValue) ---> Item Index
	Find(List,ItemValue,nColumn) ---> Search in nColumn, returns the Item Index

Example:

	aList = ["one","two","three","four","five"]
	see find(aList,"three")		# print 3

Example:

	mylist = [["one",1],
		  ["two",2],
		  ["three",3]]

	see find(mylist,"two",1) + nl		# print 2
	see find(mylist,2,2) + nl		# print 2

Also we can use the binarysearch() function to search in sorted list.

Syntax:

	BinarySearch(List,ItemValue) ---> Item Index
	BinarySearch(List,ItemValue,nColumn) ---> Search in nColumn, returns the Item Index

Example:

	aList = ["one","two","three","four","five"]
	aList = sort(aList)
	see binarysearch(aList,"three")

Output:

	five
	four
	one
	three
	two
	4

Sort

We can sort the list using the sort() function.

Syntax:

	Sort(List) ---> Sorted List
	Sort(List,nColumn) ---> Sorted List based on nColumn

Example:

	aList = [10,12,3,5,31,15]
	aList = sort(aList) see aList # print 3 5 10 12 15 31

We can sort list of strings

Example:

	mylist = ["mahmoud","samir","ahmed","ibrahim","mohammed"]
	see mylist	   	  # print list before sorting
	mylist = sort(mylist)	  # sort list
	see "list after sort"+nl
	see mylist		  # print ahmed ibrahim mahmoud mohammed samir

We can sort a list based on a specific column.

Example:

	aList = [ ["mahmoud",15000] ,
		  ["ahmed", 14000 ] ,
		  ["samir", 16000 ] ,
		  ["mohammed", 12000 ] ,
	 	  ["ibrahim",11000 ] ]

	aList2 = sort(aList,1)
	see aList2

Output:

	ahmed
	14000
	ibrahim
	11000
	mahmoud
	15000
	mohammed
	12000
	samir
	16000

Reverse

We can reverse a list using the reverse() function.

Syntax:

	Reverse(List) ---> Reversed List

Example:

	aList = [10,20,30,40,50]
	aList = reverse(aList)
	see aList 	# print 50 40 30 20 10

Insert Items

To insert an item in the list we can use the insert() function.

Syntax:

	Insert(List,Index,Item)

The inserted item will be after the index

Example:

	aList = [1,2,4,5]
	insert(aList,2,3)
	see aList	  # print 1 2 3 4 5

Nested Lists

The list may contain other lists

Example:

	aList = [ 1 , [10,20,30] , 5 , [100,1000,5000] ]
	aList2 = [
	"one","two", 
	[3,4],
	[20,30], ["three",
		  "four",
		  "five",[100,200,300]
                 ]
	]
	
	see aList[2] 	 	# print 10 20 30
	see aList[4][3] + nl 	# print 5000
	see aList2[5][2] + nl 	# print four
	see aList2[5][4][3]	# print 300

Copy Lists

We can copy lists (including nested lists) using the Assignment operator.

Example:

	aList = [
	"one","two", 
	[3,4],
	[20,30], ["three",
		  "four",
		  "five",[100,200,300]
                 ]
	]

	aList2 = aList		# Copy aList to aList2
	aList2[5] = "other"	# modify item number five
	see aList2[5] + nl	# print other
	see aList[5]		# print three four five 100 200 300

First-class lists

Lists are `first-class citizens <http://en.wikipedia.org/wiki/First-class_citizen>`_ where we can store lists in variables, pass lists to functions, and return lists from functions.

Example:

	aList = duplicate( [1,2,3,4,5] )
	see aList[10] + nl		  # print 5

	see mylist()			  # print 10 20 30 40 50
	
	func duplicate list
		nMax = len(list)
		for x = 1 to nMax
			list + list[x]
		next
		return list

	func mylist return [10,20,30,40,50]

Using Lists during definition

We can use the list items while we are defining the list for the first time.

Example:

	aList = [ [1,2,3,4,5] , aList[1] , aList[1] ]
	see aList	# print 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5

Passing Lists to Functions

Lists are passed to functions by reference, This means that the called function will work on the same list and can modify it.

Example:

	func main
		aList = [1,2,3,4,5]	# create list, local in function main
		myfunc(aList)		# call function, pass list by reference
		see aList		# print 1 2 3 4 5 6 7 8 9 10

	func myfunc list
		list + [6,7,8,9,10]

Access List Items by String Index

Instead of using numbers to determine the item index when we get item value or set item value, We can access items using string index if the item is a list contains two items and the first item is a string.

Example:

	aList = [ ["one",1] , ["two",2] , ["three",3] ]
	see aList["one"] + nl +
	    aList["two"] + nl +
	    aList["three"] 	# print 1 2 3

This type of lists can be defined in a better syntax using the : and = operators.

Example:

	aList = [ :one = 1 , :two = 2 , :three = 3 ]
	see aList["one"] + nl +
	    aList["two"] + nl +
	    aList["three"] + nl	# print 1 2 3
	see aList[1]		# print one 1

.. tip:: using : before identifier (one word) means literal

.. note:: using = inside list definition create a list of two items where the first item is the left side and the second item is the right side.

We can add new items to the list using the string index

Example:

	aList = []
	aList["Egypt"] = "Cairo"
	aList["KSA"] = "Riyadh"
	see aList["Egypt"] + nl + 	# print Cairo
	    aList["KSA"] + nl		# print Riyadh

Passing Parameters Using List

This type of lists is very good for passing parameters to functions Where the order of parameters will not be important (we can change the order).

Also some parameters maybe optional.

Example:

	myconnect (  [ :server = "myserver.com" , :port = 80 , 
                       :username = "mahmoud" , :password = "password" ] ) 

	func myconnect mypara
	
		# print connection details
		see "User Name : " + mypara[:username] + nl +
		    "Password  : " + mypara[:password] + nl +
                    "Server    : " + mypara[:server] + nl +
                    "Port      : " + mypara[:port]