1. Fall 2006AE6382 Design Computing1 Cell Arrays and Structures Learning Objectives Learn about characters, cell arrays & structures Topics Data Types Character Strings Cell Arrays Structures Summary

2. Fall 2006AE6382 Design Computing2 Storing More Than Numbers MATLAB matrices store only numeric results –What about words, names, strings? –What about arrays of arrays? MATLAB provides three more containers to store data –Character arrays –Cell arrays –Structures Examples –Gradebooks –Hierarchical geographic data

3. Fall 2006AE6382 Design Computing3 What are Character Arrays? Examples: » C = 'Hello'; %C is a 1x5 character array. » D = 'Hello there’; %D is a 1x11 character array. » A = 43; %A is a 1x1 double array. » T = 'How about this character string?’ » size(T) ans = 1 32 » whos % What do you observe? Learn?

4. Fall 2006AE6382 Design Computing4 How are Characters Stored? Character arrays are similar to vectors, except: –Each cell contains a single digit Example » u = double(T) % double is a dedicated function. » char(u) % performs the opposite function. Exercise » a = double('a') » char(a) Questions: What is the numerical value of ‘a’ and what does it mean?

5. Fall 2006AE6382 Design Computing5 Manipulating String Arrays Strings can be manipulated like arrays. Exercises » u = T(16:24) » u = T(24:-1:16) » u = T(16:24)’ » v = 'I can''t find the manual!’ % Note quote in string » u ='If a woodchuck could chuck wood,'; » v = 'how much wood could a woodchuck chuck?'; » w = [u,v] % string concatenation in Matlab » disp(u) % works just like for arrays Lessons?

6. Fall 2006AE6382 Design Computing6 Character Strings in Multiple Rows » v = ['Character strings having more than' 'one row must have the same number ‘ 'of columns just like arrays! ' ] Exercise » lawyers = char('Cochran','Shapiro','Clark','Darden'); » lawyers(3,:) Lesson? Exercise » help char » help str2mat » help strvcat Lesson?

7. Fall 2006AE6382 Design Computing7 String Construction / Manipulation >> t = ‘How about this character string?’ >> size (t) % What’s this? >> whos Lesson? >> u = double (t) >> char(u) Lesson? >>u = t(16:24) >>u = t(24:-1:16) >>u = t(16:24)’ Lesson? Page 129-131

8. Fall 2006AE6382 Design Computing8 What are Cell Arrays? Cell arrays are containers for “collections” of data of any type stored in a common container. Cell arrays are like a wall of PO boxes, with each PO box containing its own type of information. When mail is sent to a PO box the PO box number is given. Similarly each cell in a cell array is indexed. Cell arrays are created using cell indexing in the same way that data in a table or an array is created and referenced,. The difference is the use of curly braces { }.

9. Fall 2006AE6382 Design Computing9 Cell Array Access Cell arrays look a lot like Matlab arrays but they cannot generally be manipulated the same way. Cell arrays should be considered more as data “containers” and must be manipulated accordingly. (Cell arrays cannot be used in arithmetic computations like arrays can, e.g., + - * / ^) Addressing Cell Arrays: A(i,j) = {x} this is called CELL INDEXING A{i,j} = x this is called CONTENT ADDRESSING either can be used, but be careful…

10. Fall 2006AE6382 Design Computing10 Cell Array Examples first = ‘Hello’; second = {‘hello’,’world’,’from’,’me’}; third (1,1) = {‘happy’}; % Cell indexing third {2,1} = ‘birthday’; % Content addressing third {3,1} = 40; What do you observe? Lesson? >> third >> third (1,1), third {1,1} >> third (2,1), third {2,1} >> third (3,1), third {3,1}

11. Fall 2006AE6382 Design Computing11 Cell Arrays of Strings All rows in a string array MUST have the same number of columns … this is a pain. Solution? Cell arrays!!!! Next slide … but just try the following! Exercise » C = {'How';'about';'this for a';'cell array of strings?'} Question: What is different from what you have been doing before? Exercises » size(C) » C(2:3) » C([4,3,2,1]) » [a,b,c,d] = deal(C{:}) Lessons?

12. Fall 2006AE6382 Design Computing12 Cell Array Examples … contd. Exercise » C = cell(2,3) % Defines C to be a cell array » C(1,1) = {'This does work'} % ( ) refer to PO Box » C{2,3} = 'This works too’ % { } refers to contents Lesson? » A = cell(1,3) % Note 1 x 3 » A = {'My', 'name', 'is', ‘Burdell'} % Note 1 x 4 » A = {'My'; 'name'; 'is' ; ‘Burdell'} Lessons? Exercise … Important » help lists

13. Fall 2006AE6382 Design Computing13 Cell Array Examples … contd. Exercise » A = {'My'; 'name'; 'is' ; 'Farrokh'} » iscellstr(A) % logical test for a cell array of strings » ischar(A) % logical test for a string array Lesson? Exercise » help cell » help cellstr » help celldisp » B = cell(2,4) » B = {'My', 'name', 'is', Burdell; 10, 20, 30, 40} » celldisp(B) Lesson?

14. Fall 2006AE6382 Design Computing14 Cell Arrays are Simple… The basics of working with cell arrays are well explained in the Matlab documentation. Additional information can be found at the Mathworks web site: http://www.mathworks.com/

15. Fall 2006AE6382 Design Computing15 What are Structures? Numeric, character and cell arrays all reference the individual elements by number. Structures reference individual elements within each row (called “fields”) by name. To access these fields, the dot “.” notation is used. Assignment is as follows: structurename.fieldname = datatype; Text Page 115

16. Fall 2006AE6382 Design Computing16 Creating a Structure… Let’s create a simple structure: –person.firstname = ‘George’; –person.lastname = ‘Burdell’; –person.address1 = ‘803 Tech Parkway’; –person.city = ‘Atlanta’; –person.state = ‘GA’; –person.zip = ‘30332-0001’;

17. Fall 2006AE6382 Design Computing17 Structures: A Bigger Picture… Structures can hold elements in fields, which in turn contain data types. mystruc text1 numb1 text2 ‘ Hello’ [1 2 3 4] AE6382 Fall 2004 numb2 5 6 7 8

18. Fall 2006AE6382 Design Computing18 More on Structures… A structure can have a field that is a structure itself. A structure array is that which contains more than one record for each field name. As the structure array is expanded (more records are created), all unassigned fields are filled with an empty matrix. All structures have the same number of fields and elements in each field.

19. Fall 2006AE6382 Design Computing19 Example of a Structure...: student.name.first = ‘Joe’; student.name.last = ‘Smith’; student.score = 82.39; student.grade = ‘B’; student(2).name.first = ‘Anna’; student(2).name.last = ‘Lee’; student(2).score = 94.50; Student(3).name.first = ‘Jerry’; NOTE: There are other spaces to fill, but we haven’t assigned any values to these fields, so they remain as an empty matrix.

20. Fall 2006AE6382 Design Computing20 Picture of Student Grade Structure student name score grade first last Joe Smith 82.39 B Anna Lee 94.50 [ ] Jerry [ ] student(1) student(2)student(3)

21. Fall 2006AE6382 Design Computing21 Structure Resources… Structures are explained in the Matlab online documents. You can find tutorials on the web: http://www.mathworks.com/

22. Fall 2006AE6382 Design Computing22 Summary Action Items Review the lecture Review the material on the websites Learning Matlab can store and manipulate much more than simply numbers