© Bar-Ilan University Computer Center

MATLAB concepts Course

Data types MATLAB concepts

• Numeric: double (computations), single, signed and unsigned integer types • Logic (numeric) • Sparse (numeric) • Characters • Structures • Cell arrays • MATLAB and user classes (structure) • Java class • function handles

Session 2 I/O and Data types

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Strings

Characters

• String = an array of characters. • Creation in MATLAB:

• Character = a printable/readable sign, represented by a two-byte ascii code. • Creation in MATLAB:

ƒ '' will create a 1D string. Example: A = 'this is a string' ƒ char(N) where 0 < N < 65535 is the ascii code array

ƒ '' Examples: 'r' or '.' or ' ' ƒ char(N) where 0 < N < 65535 is the ascii code

• Usage of strings: ƒ Textual data ƒ Headers, title and annotation in graphics ƒ Names of files, variables and structure fields

• double(character) get ascii code of character 3

String manipulation

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String conversion

• Like any array. • Convert a number to a string: num2str • Convert an integer to a string: int2str • Convert a string to a number: str2num

ƒ Concatenation of strings ƒ Selection of characters in a string ƒ deletion of characters in a string

• blanks(n) Create a row vector of n blanks • strtrim(str) Remove leading and trailing white space from character string str. 5

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ƒ If the string does not represent a number, returns an empty array ƒ NaN is recognized

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Session 2 page 1

© Bar-Ilan University Computer Center

MATLAB concepts Course

Importing data into MATLAB

User-choice: files

• The load command: load filename • Load binary: filename without extension, assumes .mat Example: load myvars will look for a file myvars.mat and will load all variables in it. • Load ascii: filename with any extension except .mat will load one matrix. Example: load onetest.dat will create a variable named onetest. Functional form: var = load(‘file name’)

• uigetfile(FilterSpec) ƒ display a dialog box that lists files in the current directory according to FilterSpec ƒ return the user’s choice as a string.

• uigetdir ƒ Display a dialog box that lists directories in the current directory ƒ return the user’s choice as a string.

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• Read excel files: A = xlsread('file-name') • Other formats: help fileformats

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Keyboard input

Saving data to disk

• user_entry = input(prompt)

• The save command: save filename vars • Save variables in binary: assumes .mat. save filename var1 var2 var3 … save filename will save all variables. • Save numerical matrices in readable format: save name.ext var1 var2 … -ascii will print var1, var2 etc. into a file, each row in a new line. • Functional form: save('filename','var1','var2','-ascii') Demo: Strings

ƒ display the string variable prompt as a prompt on the screen ƒ Wait for input from the keyboard ƒ Interpret numeric characters as numbers and character input as variable names ƒ return the value entered in user_entry

• input_string = input(prompt,’s’) return the entered string as-is

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The plot command • • • • • • •

Colors and line-styles

plot(x,y) → default: solid line, no markers plot(y) → default: x = 1,2, … , length(y) Default color Automatic scaling Default tick marks No titles Multiple curves: If y is a matrix or x,y are matrices, each column produces a curve. 11

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Curve style: plot(x,y,'style-chars')

Colors b blue g green r red c cyan m magenta y yellow k black

Line Styles - solid -- dashed : dotted -. dot-dashed

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MATLAB concepts Course

Texts

Markers . o x +

point circle x +

* s d

star square diamond

v ^ < > p h

• • • • • •

Plot title: title('text') x-axis title: xlabel('text') y-axis title: ylabel('text') Legend: legend('text1','text2',…) Remove legend: legend off text(x,y, 'str') : Write str at data coordinates (x,y) with default properties • Adding a text does not change axis scaling.

triangle (down) triangle (up) triangle (left) triangle (right) pentagram hexagram

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Printing and saving plots

Adding and deleting curves

• Send a plot to default printer: print • Save into a file: print -device fname • Common devices: BMP 24-bit -dbmp EPS black and white -deps JPEG 24-bit -djpeg PDF Color PDF file -dpdf • Example: print -djpeg exmpl will create a file named exmpl.jpg Demo: Graphics • Functional form: print('-device','fname') Questions 1-3

• Default: every plot command overrides previous plots. • hold on: switch to adding-plots mode • hold off: switch to override mode • clf: clear figure • Default: adding curves automatically changes scaling, unless there was a userdefined scaling. 15

Cell-arrays

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Cell-array: example

• Cell array = an array whose elements are arrays themselves. • A cell can be of any type, including a cell array

C: cell 1x3 C{1}

C{2} Cell 4x1

C{3} Cell 3x2

1X10

9x4

9x2

1X12

2x2

3x2

1X8

5x7

2x7

1X6 17

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Session 2 page 3

© Bar-Ilan University Computer Center

MATLAB concepts Course

Working with cell-arrays Cell-arrays in graphic annotation

• Creation: use listing with curly brackets {} • Reference to elements in the array: C(2) • Reference to cell contents:

• Multiple-line texts: – A cell-array of strings, each cell is a text line. – Applies to text, title, xlabel and ylabel.

ƒ one level: C{2} ƒ more levels: C{3}{3,2} ƒ one level, element is an array: C{1}(5)

• Cell-array form of legend: legend({cell-array of strings})

• Concatenation: [cell1 cell2 cell3 … ] • Assignment: cell_array{index}=val 19

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User-choice: menu

Structures

• The menu command: k = menu(mtitle,opt1,opt2,...,optn) • Display the menu whose title is a string variable mtitle and whose choices are string variables opt1, opt2, and so on. • Cell-array form: k = menu(mtitle,{cell-array of strings}) • Return the index k of the selected menu item.

Structure: a collection of different kinds of data, organized by named fields. Variable name field1 field2

A field can be of any type, including a structure or a cell-array.

field3

Demo: Cell-arrays Questions 4-5

field4

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Structures - example

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Structures – creation and reference

Spectra: ST

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Clean: ST Raw: numeric 2D

Filename: string Inputs: cell 1D

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Lipid: ST

Field is an array: spectra.species(5,:) Field is a cell-array: spectra.inputs{3} Field is a structure: spectra.clean.raw

Creation ƒ

Raw: numeric 2D

by assignment var.field=value

Filename: string

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Using a command struct('field1',VAL1,'field2',VAL2,...)

Inputs: cell 1D 23

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Reference: varname.fieldname ƒ ƒ ƒ

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MATLAB concepts Course

Importdata: generalized input

Structure arrays • Structure array = array of structures with the same field names. • Reference varname(index).fieldname

• If some of the fields are missing from some of the array elements, MATLAB automatically assigns an empty matrix.

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• Creates a structure, fields depend on the type of and data in the file. • Usage: S = importdata(filename) • Excel and text files ƒ data: the largest numeric matrix ƒ textdata: all texts ƒ colheaders: column headers

• mat files: variables are fields • Others (.wav, .jpg) Demo: structures Question 6

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dir command • Returns info on all files according to FilterSpec • Usage: Flist = dir(FilterSpec) • Flist is a structure array, one structure for each file, with the following fields: name date bytes isdir datenum 27

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