CSE 123
Lecture 9
Formatted Input/Output
Operations
fprintf Function
Format effects only the display of variables not their values through program
execution
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
Modifier
Field Width
Precision
Format Descriptor
(Required)
(Optional)
(Optional)
(Optional)
(Required)
Common format specifier notation for fprintf
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
Escape characters in Format strings
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 (%)
Example: Decimal (integer) data is displayed using %d format specifier.
fprintf(‘%d\n’,123)
----|----|
123
fprintf(‘%6d\n’,123)
----|----|
123
fprintf(‘%6.4d\n’,123)
----|----|
0123
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
Example: floating point (real) data is displayed using %e, %f and %g
format specifiers
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: character data may be displayed with %c or %s format specifiers.
fprintf(‘%c\n’,‘s’)
----|----|
s
fprintf(‘%s\n’, ‘string’)
----|----|
string
fprintf(‘%8s\n’, ‘string’)
----|----|
string
fprintf(‘%-8s\n’, ‘string’)
----|----|
String
(left justified)
Examples:
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
X is 8.80 meters or 8800.000 mm
X is 7.70 meters or 7700.000 mm
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)
Binary files = Pre-converted data for computer usage.
(.bin .mat)
•Software specific format = formatted data for software usage (.xls)
Depending on the type of data file
Different import function
Importing data
test1.txt
Function load
Syntax:
load filename
load filename loads all the variables from filename
0
1.0000
2.0000
3.0000
4.0000
5.0000
6.0000
7.0000
8.0000
9.0000
10.0000
0
0.3090
0.5878
0.8090
0.9511
1.0000
0.9511
0.8090
0.5878
0.3090
0.0000
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.
>> load test1.txt;
>> whos
Name Size
test1 11x2
Bytes
Class
176 double array
Importing data
test2.txt
Function dlmread
Syntax:
7.2;8.5;6.2;6.6
5.4;9.2;8.1;7.2
A = dlmread('filename', 'delimiter');
test3.txt
7.2;
5.4;
dlmread command works even if the contents of
filename has spaces:
8.5; 6.2; 6.6
9.2; 8.1; 7.2
>> A=dlmread('test2.txt',';')
A=
7.2000
5.4000
8.5000
9.2000
6.2000 6.6000
8.1000 7.2000
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 %u for integers
[A,B,C,...] = textread('filename','format',N) reads data from the file 'filename' N times.
Importing data
test4.txt
Ann Type1 12.34 45 Yes
Joe Type2 45.67 67 No
>> [A B C D E]=textread('test4.txt',' %s %s %f %f %s')
A=
'Ann'
'Joe'
B=
'Type1'
'Type2'
C=
12.3400
45.6700
D=
45
67
E=
'Yes'
'No'
>> [A B C D E]=textread('test4.txt',' %s %s %f %f %s',1)
A=
'Ann'
B=
'Type1'
C=
12.3400
D=
45
E=
'Yes'
Importing data
Function fscanf
Syntax:
: Read formatted data from file
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
inf
[m,n]
Read at most n numbers, characters, or strings.
Read to the end of the file.
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.
Importing data
Example 1:
fid = fopen('exp.txt', 'r');
a = fscanf(fid, '%g %g', [2 inf])
a = a';
fclose(fid)
xdata.txt
% It has two rows now.
1 12 3 4 8
a =
Example 2:
clc;clear;
fileID=fopen(‘xdata.txt', 'r' );
[a,nvals]=fscanf( fileID,'%d ',inf);
fclose( fileID);
a
nvals
1
12
3
4
8
nvals =
5
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
Importing data
Data Format Sample
1234 5
6 7 8 9 10
File Extension
Matlab function
.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
Tips for loading data
Set up the PATH
Syntax:
path(path,'c:/temp');
path(path,'newpath')
View or change the MATLAB directory search
path
path(path,‘z:/ME102');
Tips for loading data
Use for loops to load entire series of files
for j=1:N
name1=‘test00';
name2=num2str(j);
name3=‘.txt’;
NAME=[name1 name2 name3];
F=load(NAME);
A(:,1)= F(:,1);
A(:,j+1)= F(:,2);
end
test001.txt
test002.txt
0
0
1.0000 0.3090
test003.txt
0
0
2.0000 1.0000
0.5878 0.3090
0
0
3.0000 2.0000
0.8090 0.5878
1.0000
0.3090
4.0000 3.0000
0.9511 0.8090
0.5878
5.0000 4.0000
1.00002.0000
0.9511
0.8090
6.0000 5.0000
0.95113.0000
1.0000
4.0000
7.0000 6.0000
0.8090 0.9511 0.9511
1.0000
8.0000 7.0000
0.58785.0000
0.8090
6.0000
9.0000 8.0000
0.3090 0.5878 0.9511
7.0000 0.8090
10.00009.0000
0.0000
0.3090
8.0000 0.5878
10.0000 0.0000
9.0000 0.3090
10.0000 0.0000
Exporting data
Function save
Syntax: save filename
save filename stores all the workspace variables in filename.mat in the
current directory
Selected variables can be saved:
save filename A B C stores the variables A B and C in filename.mat in the
current directory
Exporting data
Three Steps:
Functions fopen, fprintf and fclose
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.
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.
Exporting data
Functions fopen,fprintf and fclose
2 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.
3 fclose: close one or more open files
Syntax: fclose(fid)
Exporting data
Functions fopen, fprintf and fclose
Exp.txt
x = 0:0.1:1;
Y = [x; exp(x)];
fid = fopen('Exp.txt','w');
fprintf(fid,'%6.2f %12.8f \n',Y);
fclose(fid)
File created in
current directory
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1.00000000
1.10517092
1.22140276
1.34985881
1.49182470
1.64872127
1.82211880
2.01375271
2.22554093
2.45960311
2.71828183
Importing data (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'.
Importing data (more…)
csvlist.dat
Example: csvread
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
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
Importing data (more…)
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)
m =
5
10
15
20
25
30
7
14
21
28
35
42
11
22
33
44
55
66
Importing data (more…)
To read the matrix bounded by zero-based (2,0) and
(3,3) and assign it to m,
Example: csvread
m = csvread('csvlist.dat', 2, 0, [2,0,3,3])
m =
5
7
10
14
15
21
20
28
Exporting data (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.
Exporting data (more…)
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
Exporting data (more…)
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
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
testdata1.xls
1
6
2
7
3
8
4
9
5
10
Importing data (more…)
Example: xlsread
A = xlsread('testdata1.xls‘,-1)
A =
1
6
2
7
3
8
4
9
5
10
testdata1.xls
1
6
2
7
3
8
4
9
5
10
Importing data (more…)
Example: xlsread
A = xlsread('testdata1.xls‘,1,’A4:B5’)
A =
4
9
5
10
testdata1.xls
1
6
2
7
3
8
4
9
5
10
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')
tempdata.xls
Time
Temp
12
98
13
99
14
97