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]