1. Lists – Indexing and Sorting
Intro to Computer Science
CS1510
Dr. Sarah Diesburg

2. Homework Assignment PA07
Regular deadline is Wednesday
Remember
Follow the new design document and function commenting
Example design document
Example function commenting

3. The Python List Data Structure
A list an ordered sequence of items of any type.
myList = [1, [2,1], ‘hello’]

4. List Indexing
We can index into a list in much the same way as a string
>>> myList = [1, [2,1], ‘hello’]
>>> myList[2]
‘hello’
Let’s play with some indexing problems. Break up into teams of 2 or 3.

5. Example Program
myList = [[‘Penny’, 90], [‘Leonard’, 85], 2] print(myList[0]) print(myList[0][0][3] + myList[1][0][2]) print((myList[0][1] + myList[1][1]) / myList[2]) #What is the output of the three print statements?

6. List Methods myList.append(x) myList.extend(C) myList.pop()
myList.insert(i,x)
myList.remove(x)
myList.sort()
myList.reverse()
myList.index(x)
myList.count(x)
Which methods modify the list??

7. Sorting
Only lists have a built-in sorting method. Thus you often convert your data to a list if it needs sorting:
myLst = list(‘xyzabc’)
myLst  [‘x’,’y’,’z’,’a’,’b’,’c’]
myLst.sort()
# convert back to a string
sortStr = ‘’.join(myLst)
 ‘abcxyz’

8. Sorted Function
The sorted function will break a sequence into elements and sort the sequence, placing the results in a list:
sortLst = sorted(‘hi mom’)
 [‘ ‘,’h’,’i’,’m’,’m’,’o’]

9. Unusual Results
myLst = [4, 7, 1, 2] myLst = myLst.sort() myLst  None # what happened? What happened was the sort operation changed the order of the list in place (right side of assignment). Then the sort method returned None, which was assigned to the variable. The list was lost and None is now the value of the variable.

10. Anagram Example
Anagrams are words that contain the same letters in a different order. For example: ‘iceman’ and ‘cinema.’
A strategy to identify anagrams is to take the letters of a word, sort those letters, then compare the sorted sequences.
Anagrams should have the same sequence.

11. Anagram Program Algorithm
Input 2 words to examine.
Sort the letters of each word into a new string.
Compare the resulting sorted strings