ES 117

Formatted Input/Output

Operations

fpintf function writes formatted data in a user specified format to a file

fprintf(fid,format string,val1,val2, ….)

fid :the file id to which data will be written (no fid for printing on CW)

format :the format string. % always marks the beginning of a format

The structure of a format specifier

%-12.5e

Marker

(Required)

Field Width

(Optional)

Precision

(Optional)

Format Descriptor

(Required)

Modifier

(Optional)

Format effects only the display of variables not their values through program execution

fprintf Function

Specifier Description

%c Single character

%d Decimal notation (signed)

%e Exponential notation

%E Exponential notation

%f Fixed-point notation

%g The more compact of %e and %f. Insignificant zeros do not print

%s String of characters

%u Decimal notation unsigned

Common format specifier notation for fprintf

symbol Description

\n New line

\t Horizontal tab

\b backspace

\\b Print an ordinary backslash (\)

\‘’ or ‘’ Print an aposthrophe or single quote

%% Print an ordinary percent symbol (%)

Escape characters in Format strings

fprintf(‘%d\n’,123) ----|----|

123

fprintf(‘%6d\n’,123) ----|----|

123

fprintf(‘%6.4d\n’,123) ----|----|

0123

Example: Decimal (integer) data is displayed using %d format specifier.

If a non decimal number is displayed with the %d specifier, the specifier

will be ignored and the number will be displayed in exponential format

fprintf(‘%6d\n’,123.4) produces 1.234000e+002

fprintf(‘%f\n’,123.4) ----|----|

123.400000

(default is 6 chars after the decimal place)

fprintf(‘%8.2f\n’,123.4) ----|----|

123.40

fprintf(‘%4.2f\n’,123.4) ----|----|

123.40 (6 chars wide field)

fprintf(‘%10.2e\n’,123.4) ----|----|

1.23e+002

fprintf(‘%10.2E\n’,123.4) ----|----|

1.23E+002

fprintf('%8.4f\n',123.4) ----|----|

123.4000

fprintf('%8.4g\n',123.4) ----|----|

123.4

Example: floating point (real) data is displayed using %e, %f and %g

format specifiers

fprintf(‘%c\n’,‘s’) ----|----|

s

fprintf(‘%s\n’, ‘string’) ----|----|

string

fprintf(‘%8s\n’, ‘string’) ----|----|

string

fprintf(‘%-8s\n’, ‘string’) ----|----|

String (left justified)

Example: character data may be displayed with %c or %s format specifiers.

Data Import-Export

Why is it important?

Lab experiment results are:

usually recorded in lab (even on paper)

Put together and stored into a data file

Analyzed using mathematical tools

Text file (.txt)

Microsoft Excel file (.xls)

Binary file

What do we want to export?

Save everything in the workspace for post analysis.

Save a selected number of results from the analysis in a text file

(formatted or not)

Importing data

Two common ways

Direct input through the keyboard (using the input function)

•Good for individual input.

•Not so good for large amount of data.

Use existing data stored in a file and import them into Matlab.

•Good for any data set size.

•Need to know the format of the data.

Importing data

Different types of data files

•Text based files = formatted data for user usage. (.txt .dat )

Usually follows the American Standard Code for Information Interchange (ASCII)

Depending on the type of data file Different import function

Binary files = Pre-converted data for computer usage. (.bin .mat)

•Software specific format = formatted data for software usage (.xls)

Importing data

Function load

Syntax: load (filename)

load filename loads all the variables from filename

If filename has an extension other than .mat, load

treats the file as ASCII data.

If filename has no extension, load looks for file

named filename or filename.mat and treats it as a

binary MAT-file.

0 0

1.0000 0.3090

2.0000 0.5878

3.0000 0.8090

4.0000 0.9511

5.0000 1.0000

6.0000 0.9511

7.0000 0.8090

8.0000 0.5878

9.0000 0.3090

10.0000 0.0000

test1.txt

>> load test1.txt;

>> whos

Name Size Bytes Class

test1 11x2 176 double array

Tips for loading data

Use for loops to load entire series of files

for j=1:N

end

0 0

1.0000 0.3090

2.0000 0.5878

3.0000 0.8090

4.0000 0.9511

5.0000 1.0000

6.0000 0.9511

7.0000 0.8090

8.0000 0.5878

9.0000 0.3090

10.0000 0.0000

test001.txt

0 0

1.0000 0.3090

2.0000 0.5878

3.0000 0.8090

4.0000 0.9511

5.0000 1.0000

6.0000 0.9511

7.0000 0.8090

8.0000 0.5878

9.0000 0.3090

10.0000 0.0000

test002.txt

0 0

1.0000 0.3090

2.0000 0.5878

3.0000 0.8090

4.0000 0.9511

5.0000 1.0000

6.0000 0.9511

7.0000 0.8090

8.0000 0.5878

9.0000 0.3090

10.0000 0.0000

test003.txt

name1=‘test00';

name2=num2str(j);

name3=‘.txt’;

NAME=[name1 name2 name3];

F=load(NAME);

A(:,1)= F(:,1);

A(:,j+1)= F(:,2);

Importing data

Function dlmread

Syntax: A = dlmread('filename', 'delimiter');

dlmread command works even if the contents of

filename has spaces:

>> A=dlmread('test2.txt',';')

A =

7.2000 8.5000 6.2000 6.6000

5.4000 9.2000 8.1000 7.2000

7.2;8.5;6.2;6.6

5.4;9.2;8.1;7.2

test2.txt

7.2; 8.5; 6.2; 6.6

5.4; 9.2; 8.1; 7.2

test3.txt

Importing data

Function textread

Syntax: [A,B,C,...] = textread('filename','format')

[A,B,C,...] = textread('filename','format',N)

[A,B,C,...] = textread('filename','format') reads data from the file filename into

the variables A,B,C, and so on, using the specified format, until the entire file is

read.

textread is useful for reading text files with known mixed formats. Both fixed

and free format files can be handled.

The format needs to be specified with a specifier like fprintf

%s for string, %f for fix point notation %d for integers

[A,B,C,...] = textread('filename','format',N) reads data from the file 'filename' N

times.

Importing data

Ann Type1 12.34 45 Yes

Joe Type2 45.67 67 No

test4.txt

>> [A B C D E]=textread('test4.txt',' %s %s %f %f %s')

>> [A B C D E]=textread('test4.txt',' %s %s %f %f %s',1) A =

'Ann'

'Joe'

B =

'Type1'

'Type2'

C =

12.3400

45.6700

D =

45

67

E =

'Yes'

'No'

A =

'Ann'

B =

'Type1'

C =

12.3400

D =

45

E =

'Yes'

Data Format Sample

File Extension

Matlab function

1 2 3 4 5

6 7 8 9 10

.txt .dat

or other

load

1; 2; 3; 4; 5

6; 7; 8; 9; 10

or

1, 2, 3, 4, 5

6, 7, 8, 9, 10

.txt .dat .csv

or other

dlmread

or

csvread

Ann Type1 12.34 45 Yes

Joe Type2 45.67 67 No

.txt .dat

or other

textread

or

fscanf

Grade1 Grade2 Grade3

91.5 89.2 77.3

88.0 67.8 91.0

67.3 78.1 92.5

.txt .dat

or other

textread

or

fscanf

Importing data - Summary

Three Steps:

Functions fopen, fprintf/fscanf and fclose

Importing- Exporting data using fprintf or fscanf functions

1. fopen: opens a file or obtain information about open files

Syntax: fid = fopen(filename,permission)

Permission = 'r‘ Open file for reading (default).

'w‘ Open file, or create new file, for writing; discard existing contents, if any.

'a‘ Open file, or create new file, for writing; append data to the end of the file.

Importing - Exporting data

fopen file permissions

‘r’ Open an existing file for reading only

‘r+’ Open an existing file for reading and writing

‘w’ Delete the contents of an existing file (or create a new file) and open it for

writing only.

‘w+’

Delete the contents of an existing file (or create a new file) and open it for

reading and writing

‘a’ Open an existing file (or create a new file) and open it for writing only,

appending to the end of file.

‘a+’

Open an existing file (or create a new file) and open it for reading and

writing, appending to the end of file.

fprintf: Used the same way as display function, except that this time, the

formatting of the data is retained in the data file.

Syntax: fprintf(fid,format,A,...)

Formats the data in the real part of matrix A (and in any additional matrix

arguments) under control of the specified format string, and writes it to the

file associated with file identifier fid.

2

Exporting data

Importing data

fscanf : Read formatted data from file

Syntax: A = fscanf(fid, format)

[A,count] = fscanf(fid, format, size)

A = fscanf(fid, format) reads data from the file specified by fid, converts it

according to the specified format string, and returns it in matrix A. Argument fid is an

integer file identifier obtained from fopen. format is a string specifying the format of the

data to be read. [A,count] = fscanf(fid, format, size) reads the amount of data specified by

size, converts it according to the specified format string, and returns it along with a count

of values successfully read. size is an argument that determines how much data is read.

Options for size

n Read at most n numbers, characters, or strings.

inf Read to the end of the file.

[m,n] Read at most (m*n) numbers, characters, or strings. Fill a matrix of at most m

rows in column order. n can be inf, but m cannot.

Functions fopen, fscanf/fprintf and fclose

fclose: close one or more open files

Syntax: fclose(fid)

3

Importing - Exporting data

Exporting data

x = 0:0.1:1;

Y = [x; exp(x)];

0.00 1.00000000

0.10 1.10517092

0.20 1.22140276

0.30 1.34985881

0.40 1.49182470

0.50 1.64872127

0.60 1.82211880

0.70 2.01375271

0.80 2.22554093

0.90 2.45960311

1.00 2.71828183

Exp.txt

Functions fopen, fprintf and fclose

File created in

current directory fid = fopen('Exp.txt','w');

fprintf(fid,'%6.2f %12.8f \n',Y);

fclose(fid)

Importing data

Example 1:

fid = fopen('exp.txt', 'r');

a = fscanf(fid, '%f %f', [2 inf]) % It has two rows now.

a = a';

fclose(fid)

0 1

0.1 1.10517092

0.2 1.22140276

0.3 1.34985881

0.4 1.4918247

0.5 1.64872127

0.6 1.8221188

0.7 2.01375271

0.8 2.22554093

0.9 2.45960311

1 2.71828183

1 12 3 4 8 xdata.txt

Example 2:

clc;clear;

fileID=fopen(‘xdata.txt', 'r' );

[a,nvals]=fscanf( fileID,'%d ',inf);

fclose( fileID);

a

nvals

a =

1

12

3

4

8

nvals =

5

Importing data (more…)

Function xlsread reads MS Excel files

Syntax: num = xlsread(filename)

num = xlsread(filename, -1)

num = xlsread(filename, sheet, 'range‘ )

num = xlsread(filename) returns numeric data in double array num from the

first sheet in the Microsoft Excel spreadsheet file named filename. The filename

argument is a string enclosed in single quotes.

num = xlsread(filename, -1) opens the file filename in an Excel window,

enabling you to interactively select the worksheet to be read and the range of

data on that worksheet to import.

num = xlsread(filename, sheet, 'range') reads data from a specific rectangular

region (range) of the worksheet specified by sheet.

Importing data (more…)

Example: xlsread

A = xlsread('testdata1.xls')

A =

1 6

2 7

3 8

4 9

5 10

1 6

2 7

3 8

4 9

5 10

testdata1.xls

Importing data (more…)

Example: xlsread

A = xlsread('testdata1.xls‘,-1)

A =

1 6

2 7

3 8

4 9

5 10

1 6

2 7

3 8

4 9

5 10

testdata1.xls

Importing data (more…)

Example: xlsread

A = xlsread('testdata1.xls',1, 'A4:B5')

A =

4 9

5 10

1 6

2 7

3 8

4 9

5 10

testdata1.xls

Exporting data (more…)

Function xlswrite

Syntax: xlswrite(filename, M)

xlswrite(filename, M, sheet, 'range')

xlswrite(filename, M) writes matrix M to the Excel file filename. The filename input is a

string enclosed in single quotes. The input matrix M is an m-by-n numeric, character, or

cell array, where m < 65536 and n < 256. The matrix data is written to the first worksheet

in the file, starting at cell A1.

xlswrite(filename, M, sheet, 'range') writes matrix M to a rectangular region specified by

range in worksheet sheet of the file filename.

Exporting data (more…)

Example: xlswrite

xlswrite('testdata', [12.7 5.02 -98 63.9 0 -.2 56])

d = {'Time', 'Temp'; 12 98; 13 99; 14 97};

s = xlswrite('tempdata.xls', d, 'Temperatures', 'E1')

Time Temp

12 98

13 99

14 97

tempdata.xls

The Import Wizard

To import ASCII data, you must know how the data in the file

is formatted.

For example, many ASCII data files use a fixed (or uniform)

format of rows and columns.

3-84

(continued …)

The Import Wizard (continued)

For these files, you should know the following.

• How many data items are in each row?

• Are the data items numeric, text strings, or a mixture of

both types?

• Does each row or column have a descriptive text header?

• What character is used as the delimiter, that is, the

character used to separate the data items in each row? The

delimiter is also called the column separator.

(continued …) 3-85

The Import Wizard (continued)

You can use the Import Wizard to import many types of ASCII

data formats, including data on the clipboard. When you use the

Import Wizard to create a variable in the MATLAB workspace, it

overwrites any existing variable in the workspace with the same

name without issuing a warning.

The Import Wizard presents a series of dialog boxes in which you:

1. Specify the name of the file you want to import,

2. Specify the delimiter used in the file, and

3. Select the variables that you want to import.

3-86