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CSE 123 Lecture Lecture 99

FFormatted Input/Output ormatted Input/Output OperationsOperations

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

fprintf(fid,format,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

fprintffprintf Function Function

SpecifierSpecifier DescriptionDescription

%c%c Single characterSingle character

%d%d Decimal notation (signed)Decimal notation (signed)

%e%e Exponential notationExponential notation

%E%E Exponential notationExponential notation

%f%f Fixed-point notationFixed-point notation

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

%s%s String of characters String of characters

%u%u Decimal notation unsignedDecimal notation unsigned

Common format specifier notation for fprintf

symbolsymbol DescriptionDescription

\n\n New lineNew line

\t\t Horizontal tabHorizontal tab

\b\b backspacebackspace

\\b\\b Print an ordinary backslash (\)Print an ordinary backslash (\)

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

%%%% Print an ordinary percent symbol (%)Print an ordinary percent symbol (%)

Escape characters in Format strings

fprintf(‘%d\n’,123)fprintf(‘%d\n’,123) ----|----|----|----|

123123

fprintf(‘%6d\n’,123)fprintf(‘%6d\n’,123) ----|----|----|----|

123123

fprintf(‘%6.4d\n’,123)fprintf(‘%6.4d\n’,123) ----|----|----|----|

01230123

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)fprintf(‘%f\n’,123.4) ----|----|----|----|

123.400000 123.400000

(default is 6 chars after the decimal (default is 6 chars after the decimal place)place)

fprintf(‘%8.2f\n’,123.4)fprintf(‘%8.2f\n’,123.4) ----|----|----|----|

123.40123.40

fprintf(‘%4.2f\n’,123.4)fprintf(‘%4.2f\n’,123.4) ----|----|----|----|

123.40 (6 chars wide field)123.40 (6 chars wide field)

fprintf(‘%10.2e\n’,123.4)fprintf(‘%10.2e\n’,123.4) ----|----|----|----|

1.23e+0021.23e+002

fprintf(‘%10.2E\n’,123.4)fprintf(‘%10.2E\n’,123.4) ----|----|----|----|

1.23E+0021.23E+002

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

123.4000123.4000

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

123.4123.4

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

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

s s

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

stringstring

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

stringstring

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

String (left justified)String (left justified)

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

x = 0:.1:1;

y = [x; exp(x)];

%fid = fopen('exp.txt', 'wt');

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

%fclose(fid)

fprintf( ...

'A unit circle has circumference %g radians.\n', 2*pi)

A unit circle has circumference 6.283186 radians.

B = [8.8 7.7; 8800 7700]

fprintf(1, 'X is %6.2f meters or %8.3f mm\n', 9.9, 9900, B)

X is 9.90 meters or 9900.000 mm



Examples:

Data Import-ExportData 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 dataImporting 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.


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)


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


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;6.65.4;9.2;8.1;7.2

test2.txt

7.2; 8.5; 6.2; 6.65.4; 9.2; 8.1; 7.2

test3.txt


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 %u for integers

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


Ann Type1 12.34 45 YesJoe 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')

>> [A B C D E]=textread('test4.txt',' %s %s %f %f %s',1)>> [A B C D E]=textread('test4.txt',' %s %s %f %f %s',1)A = 'Ann' 'Joe'B = 'Type1' 'Type2'C = 12.3400 45.6700D = 45 67E = 'Yes' 'No'

A = 'Ann'B = 'Type1'C = 12.3400D = 45E = 'Yes'


Function 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 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.


Example 1:

fid = fopen('exp.txt', 'r');a = fscanf(fid, '%g %g', [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 8xdata.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

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; 56; 7; 8; 9; 10 or 1, 2, 3, 4, 56, 7, 8, 9, 10

.txt .dat .csv or other

dlmread

orcsvread

Ann Type1 12.34 45 YesJoe Type2 45.67 67 No

.txt .dat or other

textread or

fscanf

Grade1 Grade2 Grade391.5 89.2 77.388.0 67.8 91.067.3 78.1 92.5

.txt .dat or other

textread

or fscanf


path(path,'c:/temp');

Tips for loading dataTips for loading data

Set up the PATH

Syntax: path(path,'newpath')

View or change the MATLAB directory search path

path(path,‘z:/ME102');

Tips for loading dataTips 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);

Function save

Syntax: save filename

save filename stores all the workspace variables in filename.mat in the current directory

Exporting dataExporting data

Selected variables can be saved:

save filename A B C stores the variables A B and C in filename.mat in the current directory

Three Steps:

Functions fopen, fprintf and fclose


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.

1


fopen file permissions

‘‘r’r’ Open an existing file for Open an existing file for reading onlyreading only

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

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

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

‘‘a’a’ Open an existing file (or create a new file) and open it for writing only, Open an existing file (or create a new file) and open it for writing only, appending to the end of file.appending to the end of file.

‘‘a+’a+’ Open an existing file (or create a new file) and open it for reading and Open an existing file (or create a new file) and open it for reading and writing, appending to the end of file.writing, appending to the end of file.

Functions fopen,fprintf and fclose

Exporting data Exporting data

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.

fclose: close one or more open files

Syntax: fclose(fid)

2

3


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 dataImporting data (more…)(more…)

Function csvread

Syntax: M = csvread(filename)

M = csvread(filename, row, col)

M = csvread(filename, row, col, range)

M = csvread(filename) reads a comma-separated value formatted file, filename. The filename input is a string enclosed in single quotes. The result is returned in M. The file can only contain numeric values.

M = csvread(filename, row, col) reads data from the comma-separated value formatted file starting at the specified row and column. The row and column arguments are zero based, so that row=0 and col=0 specify the first value in the file.

M = csvread(filename, row, col, range) reads only the range specified. Specify range using the notation [R1 C1 R2 C2] where (R1,C1) is the upper left corner of the data to be read and (R2,C2) is the lower right corner. You can also specify the range using spreadsheet notation, as in range = 'A1..B7'.


Example: csvread 02, 04, 06, 08, 10, 12 03, 06, 09, 12, 15, 18 05, 10, 15, 20, 25, 30 07, 14, 21, 28, 35, 42 11, 22, 33, 44, 55, 66

csvlist.dat

csvread('csvlist.dat')

ans =

2 4 6 8 10 12

3 6 9 12 15 18

5 10 15 20 25 30

7 14 21 28 35 42

11 22 33 44 55 66


Example: csvread

m = csvread('csvlist.dat', 2, 0)

m =

5 10 15 20 25 30

7 14 21 28 35 42

11 22 33 44 55 66

To read the matrix starting with zero-based row 2, column 0, and assign it to the variable m,


Example: csvread

m = csvread('csvlist.dat', 2, 0, [2,0,3,3])

m =

5 10 15 20 7 14 21 28

To read the matrix bounded by zero-based (2,0) and (3,3) and assign it to m,

ExExporting dataporting data (more…)(more…)

Function csvwrite

Syntax: csvwrite(filename,M)

csvwrite(filename,M,row,col)

csvwrite(filename,M) writes matrix M into filename as comma-separated values. The filename input is a string enclosed in single quotes.

csvwrite(filename,M,row,col) writes matrix M into filename starting at the specified row and column offset. The row and column arguments are zero based, so that row=0 and C=0 specify the first value in the file.


Example: csvwrite

m = [3 6 9 12 15; 5 10 15 20 25; ...

7 14 21 28 35; 11 22 33 44 55];

csvwrite('csvlist.dat',m)

type csvlist.dat

3,6,9,12,15

5,10,15,20,25

7,14,21,28,35

11,22,33,44,55


Example: csvwrite

m = [3 6 9 12 15; 5 10 15 20 25; ...

7 14 21 28 35; 11 22 33 44 55];

csvwrite('csvlist.dat',m,0,2)

type csvlist.dat

,,3,6,9,12,15

,,5,10,15,20,25

,,7,14,21,28,35

,,11,22,33,44,55

ImImporting dataporting data (more…)(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.


Example: xlsread

A = xlsread('testdata1.xls')

A =

1 6

2 7

3 8

4 9

5 10

1 62 73 84 95 10

testdata1.xls


Example: xlsread

A = xlsread('testdata1.xls‘,-1)

A =

1 6

2 7

3 8

4 9

5 10

1 62 73 84 95 10

testdata1.xls


Example: xlsread

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

A =

4 9

5 10

1 62 73 84 95 10

testdata1.xls


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.


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

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