Cell Arrays Lecture 2/8/2010 1. Data Types (Review) 2. General Concept 3. Using Cell-Arrays 1....

Cell ArraysLecture 2/8/2010

1. Data Types (Review)

2. General Concept

3. Using Cell-Arrays1. Syntax/Symbols

2. Dialog Boxes

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1. Data Types Recall your workspace. We have currently seen 4 types of

data. They are called:

Chapter 7 teaches how to operate more specifically with the cell array

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2. General Concepts

Still an array Still has to be rectangular BUT:

Each cell is more of a CONTAINER rather than one single element

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This is just a nice picture. It still has to be rectangular. :o) But the container itself can be empty, have different data types, different content inside…

General Concepts, cont.

“Cells” are a structure used by MATLAB. They…

• can contain any data type: string, integer, float, another cell

• may be mixed within an array (unlike strings, integers, and floats)

• are used with many library functions to provide a “use anything” format

• use a slightly different syntax for creating, deleting, and referencing

“Cell Arrays” are exactly that – arrays of “cells” 4

Quick Vocabulary

Parentheses ( )

Brackets [ ]

Braces { }

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3. Using Cell Arrays

Creating cell arrays:

>> C = {1, 2, 'abc', 3.4}

C =

[1] [2] 'abc' [3.4000]

Note the braces – not parentheses, not brackets!

Note how numbers in cells are displayed with brackets

But strings are not!6

Cell Arrays, cont.

Building cell arrays (i.e. concatenating)– let’s try braces:

C = {C, 'def'}

C =

{1x4 cell} 'def'

Wrong technique! Building cell-arrays uses a different syntax!

HUH?! What’s that?

Notice the curly braces? That indicates that we added a string OUTSIDE of the cell-array – we put the cell array INTO another cell-array! NOT what we wanted!!

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Cell Arrays, cont.To build a cell array:

>> C = {1, 2, 'abc'}

C =

[1] [2] 'abc'

>> C = [C, 3.45]

C =

[1] [2] 'abc' [3.4500]

1st: Create the cell array – it can even be an empty cell array, if you wish

2nd: Build as you would with normal arrays: use brackets

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Cell Arrays, cont.Referencing cell arrays:There are two ways to reference a cell array.

One way gets the entire cell. Think of it like getting an M&M: the nice gooey inside is wrapped in a hard candy…

>> x = C(1) %like old times, regular parentheses

x =

[2]The gooey inside (the “2”) is wrapped in brackets. Is this a problem? Let’s try to use it…

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Cell Arrays, cont.>> y = x + 5??? Undefined function or method 'plus' for input arguments of type 'cell'.

MATLAB says that we’re trying to add to a “cell”

Oops – I guess the candy covering was too hard

We want to add to the contents of the cell – we need to peel off that coating

To do that, use curly braces – get just the contents, not the coating (“wrapper”)

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Cell Arrays, cont.

>> x = C{1} %access INSIDE the cell

x =

2

>> y = x + 5

y =

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So using braces {} is the second way to reference a cell array. However, this time it accesses the CONTENT.

Normally, you will want to use the braces so that you get the value inside the “wrapper”.

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Cell Arrays, cont.Use braces also to replace elements – ‘cause you’re

leaving the wrapper but changing the gooey center:

>> C{1} = 5 %change 1st to 5

C =

[5] 'abc' [3.4500]

>> C{2} = 'def' %change 2nd to %string ‘def’

C =

[5] 'def' [3.4500]

>> C %pre-built array

C =

[2] 'abc' [3.4500]

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Cell Arrays, cont.

But when deleting elements from cell arrays, you want to get rid of the entire cell – including the wrapper. So use parentheses:

>> C(1) = [] %delete the first container

C =

'def' [3.4500]

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The same rule applies to these arrays. You can delete elements as long as the overall array remains rectangular! There is no deleting one cell from a 2 dimensional cell-array!

Cell Arrays, cont.

WOW! Cell arrays have many different syntaxes:

Creating: Braces { }Building: Brackets [ ]Referencing: Braces { }Replacing: Braces { }Deleting: Parentheses ()

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USING CELL ARRAYS

1. Tables of data

2. GUI (Graphical User Interfaces)

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Real life#1 - tables One of last year’s project calculated the friction of a stunt man on a

surface. However, the user had the choice to choose two surfaces (the clothing the stuntman wore, and the material he/she was sliding to), and whether it was a dry or wet surface. All was contained in 1 variable:

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Material 1 Material 2

leather leather

leather concrete

leather wood

leather clay

leather weed

Friction

dry wet

0.9 0.1

0.7 0.4

0.8 0.3

0.6 0.2

0.61 0.52

strings.. Numerical data..

Strings..

A BIG CELL-ARRAY!

Real life #2 - GUI

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Dialog Boxes

Dialog boxes are “popup windows” that allows us another means to communicate with the user.

There are dialog boxes to collect input:

inputdlg(), listdlg(), menu(), questdlg()

And there are dialog boxes to produce output:

msgbox(), warndlg()

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Dialog Boxes, cont.

Dialog boxes can be:

Modal (“waiting”) – they prevent the program from continuing until the box is closed

Non-modal (“non-waiting”) – the program continues execution while the box remains open

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Dialog Boxes, cont.

Input boxes are generally modal – we want the program to wait for input before continuing. This isn’t changeable.

Output boxes default to non-modal (“non-waiting”) but can be made modal.

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Dialog Boxes, cont.

Input dialog boxes: Collect information from the user

inputdlg() – much like the input() function, except there can be multiple prompts and multiple values provided by the user. ALL user-provided information is returned as a cell array of strings.

That’s why you need to learn cell-arrays!21

Dialog Boxes, cont.

inputdlg()

Required Arguments:1: Cell array of strings: This is the set of prompts for the user

prompts={'Coeff "a":', 'Coeff "b":', 'Coeff

"c":'}

Return Values:1: Cell array of strings: What the user provided in the boxes

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Dialog Boxes, cont.

Example code:

prompts={'Coeff "a":', 'Coeff "b":', 'Coeff "c":'};

coeffs = inputdlg(prompts);

If you are collecting numbers, you will probably use str2double() to convert the cell array into a vector:

coeffs = str2double(coeffs);

Note that the prompt strings are stored in a cell array…Does the variable have to be “prompts”?

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Dialog Boxes, cont.Example program: Quadratic Formula

clearclcprompts={'Coeff "a":', 'Coeff "b":', 'Coeff "c":'};a = 0; b = 2; c = 3; %wrong values to make loop run once % No imaginary roots, or invalidwhile ((b*b - 4*a*c) < 0 || a==0)

% Collect the coeff’s from the user coeffs = inputdlg(prompts); coeffs = str2double(coeffs); a = coeffs(1); b = coeffs(2); c = coeffs(3); end

%calculate rootsroots(1) = (-b + sqrt(b*b-4*a*c))/(2*a)roots(2) = (-b - sqrt(b*b-4*a*c))/(2*a)

Extract the values from the vector: Do we have to do this, or did we do it for convenience?

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Dialog Boxes, cont.

MATLAB figures (various types of windows: dialog boxes, plots, etc) have many, many options available to them: position, size, resizable, etc.

If you want to do more than fundamental dialog boxes, you will need to study the MATLAB help documentation.

F1 = Help

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