# 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

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

Syntax:

`	Add(List,Item)`

Example:

```	aList = ["one","two"]

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 + nl +
"KSA   : " + aList + 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 = "one" aList = "two" aList = "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 	 	# print 10 20 30
see aList + nl 	# print 5000
see aList2 + nl 	# print four
see aList2	# 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 = "other"	# modify item number five
see aList2 + nl	# print other
see aList		# 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 + 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 , aList ]
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		# 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"
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 ,