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Using Import Functions with Text Data

To import text data from the command line or in an M-file, you must use one of the MATLAB import functions. Your choice of function depends on how the data in the text file is formatted.

The text data must be formatted in a uniform pattern of rows and columns, using a text character, called a delimiter or column separator, to separate each data item. The delimiter can be space, comma, semicolon, tab, or any other character. The individual data items can be alphabetic or numeric characters or a mix of both.

The text file can also contain one or more lines of text, called header lines, or can use text headers to label each column or row. The following example illustrates a tab-delimited text file with header text and row and column headers.

To find out how your data is formatted, view it in a text editor. After you determine the format, scan the data format samples in Table 6-1 and look for the sample that most closely resembles the format of your data. Read the topic referred to in the table for more information.

 

Table 6-1: ASCII Data File Formats and MATLAB Import Commands  
Data Format Sample
 File Extension
 Description
1 2 3 4 5
6 7 8 9 10
 .txt
.dat
or other
 See Importing Numeric Text Data for more information. You can also use the Import Wizard for this data format. See Using the Import Wizard with Text Data for more information.
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
 See Importing Delimited ASCII Data Files for more information. You can also use the Import Wizard for this data format. See Using the Import Wizard with Text Data for more information.
Ann Type1 12.34 45 Yes
Joe Type2 45.67 67 No
 .txt
.dat
or other
 See Importing Numeric Data with Text Headers for more information.
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
 See Importing Numeric Data with Text Headers for more information. You can also use the Import Wizard for this data format. See Using the Import Wizard with Text Data for more information.

If you are familiar with MATLAB import functions but are not sure when to use them, view Table 6-2, which compares the features of each function.

Table 6-2: ASCII Data Import Function Feature Comparison

Function
 Data Type
 Delimiters
 Number of Return Values
 Notes
csvread
 Numeric data
 Only commas
 One
 Primarily used with spreadsheet data. See also the binary format spreadsheet import functions.
dlmread
 Numeric data
 Any character
 One
 Flexible and easy to use.
fscanf
 Alphabetic and numeric; however, both types returned in a single return variable
 Any character
 One
 Part of low-level file I/O routines. Requires use of fopen to obtain file identifier and fclose after read.
load
 Numeric data
 Only spaces
 One
 Easy to use. Use the functional form of load to specify the name of the output variable.
textread
 Alphabetic and numeric
 Any character
 Multiple return values.
Flexible, powerful, and easy to use. Use format string to specify conversions.

  Using the Import Wizard with Text Data Importing Numeric Text Data