CMPS 1371
Introduction to Computing
for Engineers
FILE Input / Output
File Input and Output
Reading from a source
Writing to a destination
Reading and Writing Data from
Files
 Some
common types of data
files are
mat
dat
txt
xls
jpg
Load and Save commands
• The highest (most abstract) level of file
I/O operations works with the entire
MATLAB workspace, or with individual
variables.
>>save demo1
>>help save
or
or
>>load demo1
>>help load
Save and Load
 Let’s try this
Review the HELP descriptions for save and
load.
 Create several variables,
 Save them to disk,
 Clear memory,
 Load one of the variables

Data Import and Export
 The next lower level of file I/O describes working
with entire files at once, but files whose contents
are not explicitly MATLAB variables.
 For example, working with spreadsheets, images,
audio, and video files, or raw ASCII text.
 MATLAB provides numerous functions to help in
working with these different formats.
>> help fileformats
Numeric Data Files
 It is common to encounter files that contain columns
and rows of numeric data
 numbers have different precisions and formats
 delimiters (spaces, tabs, ;) separate columns
Space delimiter
Comma delimiter
1
5.00 -2.3465600e+000
1, 5.00, -2.3465600e+000
1
5.20 -2.3658827e+000
1, 5.20, -2.3658827e+000
1
5.40 -2.3559947e+000
1, 5.40, -2.3559947e+000
1
5.60 -2.3716188e+000
1, 5.60, -2.3716188e+000
1
5.80 -2.3921178e+000
1, 5.80, -2.3921178e+000
Numeric Data Files
Command:
dlmread( ) - read data from a text file
Specify a delimiter
Examples:
>> data = dlmread(‘file.txt’,‘ ’);
>> data1= dlmread(‘file.dat’,‘;’,range);
>> help dlmread
YR
2007
2007
2007
2007
2007
2007
2007
2007
2007
MO
9
9
9
9
9
9
9
9
9
DAY
14
14
14
14
14
14
14
14
14
ID
145921
146250
146318
146822
146903
147002
147218
147445
147496
HRS
5
2
9
6
6
3
4
7
5
RATE
$6.50
$5.25
$8.75
$7.25
$6.25
$9.00
$6.75
$7.00
$8.50
PAY
$32.50
$10.50
$78.75
$43.50
$37.50
$27.00
$27.00
$49.00
$42.50
Specify a range of data
within file to read
Text Data Files
 When the data file contains text, dlmread( )
cannot handle it properly
 One solution is to use importdata( ) which is
described in the fileformats help info.
importdata( ) will separate the text columns and
the numeric columns into separate fields in a
structure.
 The contents of the structure can be copied into
numeric variables for analysis.

>> a = importdata(‘file.txt’,‘ ’,headerline);
>>
Spreadsheet Data
 xlsread( ) - read data from an Excel
spreadsheet
>> m = xlsread(‘file.xls’);
>> [a,b] = xlsread(‘file.xls’);
>> help xlsread
 Let’s try:




Numbers in a and text in b
Create a spreadsheet with Excel,
Explore various forms of xlsread( ) function,
How are data stored in MATLAB? What about column
and row names? What about the formulas?
Check out the xlsfinfo( ) function
Import Wizard
 Use the import
wizard to
determine the
data type and to
suggest ways to
represent the
data
 Launch from the
file menu
Exporting Data
 Use the save function for .mat or .dat
files
 Use specialized functions for other file
types
 For example
 xlswrite for Excel files
Importing and Exporting Data
 MATLAB includes a number of
specialized import functions optimized
for a variety of file formats
 Companion functions allow data to be
exported in the same file formats