Data Import/Export (MATLAB Environment)

MATLAB Environment

Data Import/Export

These topics provide information on importing and exporting data with MATLAB:

Importing Data into MATLAB

You can introduce data from other programs into MATLAB using several methods. The best method for importing data depends on the amount and format of the data.


Method	When to Use
Enter data as an explicit list of elements	If you have a small amount of data, it is easy to type the data explicitly using brackets (`[` `]`).
Create data in an M-file	Use a text editor to create an M-file that enters the data as an explicit list of elements. Use your text editor to change the data and to fix mistakes. Then just rerun the M-file to re-enter the data.
Load data from an ASCII data file (`load`)	An ASCII data file stores the data in ASCII form, with each row having the same number of values, and terminating with new lines (carriage returns), with spaces separating the numbers. Edit ASCII data files using a normal text editor. Read ASCII data files directly into MATLAB using the `load` function. This creates a variable whose name is the same as the filename. Use `dlmread` if you need to specify alternate value delimiters.
Read data using `fopen`, `fread`, and MATLAB's file I/O functions	Use these commands to load data files from other applications that have their own established file formats. These functions are discussed in detail in Chapter 15 of Using MATLAB.
Use a specialized file reader function for application-specific formats	`dlmread`	Read ASCII data file.
	`textread`	Read string and numeric data from a file into MATLAB variables using conversion specifiers.
	`wk1read`	Read spreadsheet (`WK1`) file.
	`imread`	Read image from graphics file.
	`auread`	Read Sun (`.au`) sound file.
	`wavread`	Read Microsoft WAVE (`.wav`) sound file.
Develop a MEX-file to read the data	Use this method if C or Fortran routines are already available for reading data files from other applications. See the MATLAB Application Program Interface Guide for more information.
Develop a Fortran or C translation program	Develop a program to translate your data into MAT-file format and then read the MAT-file into MATLAB with the load command. See the MATLAB Application Program Interface Guide for more information.

Exporting Data from MATLAB

There are several methods for getting MATLAB data to other applications:


Method	When to Use
Use the `diary` command	For small arrays, use the `diary` command to create a diary file and display the variables, echoing them into this file. Use your text editor to edit the diary file, removing unwanted text.
Save the data in ASCII form	Use the `save` command with the `-ascii` option. See Loading and Saving the Workspace for details on `save`. You can also use `dlmwrite` if you need to specify alternate value delimiters.
Write the data in a special format	Use `fwrite` and the other low-level I/O functions to write data files in the formats required by other applications. These functions are discussed in detail in Chapter 15 of Using MATLAB.
Use a specialized file write function for application-specific formats	`dlmwrite`	Write ASCII data file.
	`wk1write`	Write spreadsheet (`WK1`) file.
	`imwrite`	Write image to graphics file.
	`auwrite`	Write Sun (`.au`) sound file.
	`wavwrite`	Write Microsoft WAVE (`.wav`) sound file.
Develop a MEX-file to write the data	Use this method if C or Fortran routines are already available for writing data files in the form needed by other applications. See the MATLAB Application Program Interface Guide for more information.
Write out the data as a MAT-file	Use the `save` command, and then write a program in Fortran or C to translate the MAT-file into the desired format. See the MATLAB Application Program Interface Guide for more information.

Exchanging Data Files Between Platforms

It is sometimes necessary to work with MATLAB implementations on different computer systems, or to transmit MATLAB applications to users on other systems. MATLAB applications consist of M-files, containing functions and scripts, and MAT-files, containing binary data. Both types of files can be transported directly between different computers:

M-files consist of ordinary text. They are machine independent. While different platforms terminate lines with various combinations of CR (carriage return) and LF (line feed) characters, MATLAB tolerates all possible combinations. (However, text editors and other tools may not work correctly with M-files from other platforms.)

MAT-files are binary and machine dependent, but they can be transported between machines because they contain a machine signature in the file header. MATLAB checks the signature when it loads a file and, if a signature indicates that a file is foreign, performs the necessary conversion.

To use MATLAB across different platforms, you need a program for exchanging both binary and text data between the machines. When using these programs, be sure to transmit MAT-files in binary file mode and M-files in ASCII file mode. Failure to set these modes correctly usually corrupts the data.

The diary Command

Use diary to create a verbatim copy of your MATLAB session in a disk file (excluding graphics). View and edit the resulting text file using any word processor. To stop recording the session, use diary off.

[ Previous | Help Desk | Next ]