1. Advanced Data Import & Export Jeff Henrikson (jhenriks@umd.edu)
Lecture 13
Advanced Data Import & Export
Jeff Henrikson 1

2. Outline File I/O uiimport import/export Excel 2
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3. File I/O .txt .xls .mat .txt .xls .mat Read from Write to MATLAB
Problem areas:
Mixing character strings and numbers
Reading and writing formatted data a b
0.0
288.15
11.0
216.65
Show file extension:
Finder -> Preferences... -> Advanced  -> check box "Show all file extensions"
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4. Import/Export ASCII File
ASCII File with Known Data Format:
Import Export
csvread
dlmread
textscan
textread
fscanf
csvwrite
dlmwrite
Cell Array
{..} – access
cellplot – visualize
celldisp – display
File with Unknown Data Format:
uiimport Import Wizard
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5. Read URL data
urlread reads in as an array of all single characters from the http url source file that contains both data and formatting text
Work around data structure
strfind – find one string within another
length – get the length of a vector
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6. Data (mht=>txt=>xml)
Convert mht to txt data
File/Save as type: Text File
Then delete any content not needed
Or copy the needed content to Notepad
Convert txt to xml data
Microsoft Office Excel
File/Open… .txt
Delimited Next> Tab & Space Finish
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7. Export to Excel We want to save the following table to an Excel file
General format:
xlswrite (filename, variable, Sheet, Range)
216.65
11.0
288.15
0.0 b a
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8. Excel Data Structure xlswrite (filename, variable, Sheet, Range) 8
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9. Excel Data Structure xlswrite (filename, variable, Sheet, Range)
Range = B1
Data will be written starting at cell B1, taking up as many rows and columns as required.
Range = D3:G8
Data will be written in the box with corners specified by D3 and G8. Extra data will be discarded.
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10. Export to Excel Example
Open new M-file and save as L13E1.m
close; clear; clc;
% Define 2 column vectors a and b
a=[0.0; 11.0];
b=[288.15; ];
216.65 11
288.15 b a
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11. Export to Excel Example
% Write the header in the specified location
xlswrite ('L13E1.xls', 'a', 'Sheet1', 'A1');
xlswrite ('L13E1.xls', 'b', 'Sheet1', 'B1');
% Write data in the specified location
xlswrite ('L13E1.xls', a, 'Sheet1', 'A2');
xlswrite ('L13E1.xls', b, 'Sheet1', 'B2');
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12. View Example Excel Output
Current Directory Window
Right click
Open Outside MATLAB
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13. Write headers to Excel In L13E1.m we wrote 1-character headers
Let’s try writing nicer headers
216.65 11
288.15 b a
Height
Temperature
Level 1
288.15
Level 2 11
216.65
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14. Write headers to Excel
MATLAB will write each character in a separate cell!
We have to write text strings as cells, not arrays
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15. Excel header Example Open new M-file and save as L13E2.m
close; clear; clc;
% Define 2 column vectors a and b
a=[0.0; 11.0];
b=[288.15; ];
216.65 11
288.15 b a
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16. Create Excel header Cell
Create a cell array
with all headers
% First create a 3x3 empty cell array
head = cell (3,3);
% Then fill cells with row and column headers
head{1,2} = 'Height';
head{1,3} = 'Temperature';
head{2,1} = 'Level 1';
head{3,1} = 'Level 2';
Height
Temperature
Level 1
Level 2
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17. Excel header Example % Assign the Excel file name for output
filename = 'L13E2.xls';
% Write headers to Excel file
xlswrite(filename, head, 'Sheet1', 'A1');
% Write data to Excel file
xlswrite(filename, a, 'Sheet1', 'B2');
xlswrite(filename, b, 'Sheet1', 'C2');
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18. View Example Excel Output
Current Directory Window
Right click
Open Outside MATLAB
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19. Import from Excel >>uiimport [Enter]
Browse and select file L13E2.xls
Click Names to preview data
Check boxes to select data
Click Finish
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20. uiimport Numeric variables are imported as array 'data'
Text strings are imported as cells 'textdata'
If you check Generate M-code, MATLAB will create an M-File to read the data.
Next time, you can just type:
>>importfile ('L13E2.xls') [Enter]
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21. Import from Excel In Command Window >> whos [Enter]
Name Size Bytes Class Attributes
data 2x double
textdata 3x cell
>> data [Enter]
data =
>> textdata [Enter]
textdata =
'' 'Height' 'Temperature'
'Level 1' '' ''
'Level 2' '' ''
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22. Import from Excel uiimport works well if you have a single file
Multiple data files: read data from inside the M-file
(like textscan)
Command to use: xlsread
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23. Import with xlsread >> mydata = xlsread ('L13E2.xls', 'Sheet1');
>> [mydata, header] = xlsread ('L13E2.xls', 'Sheet1')
mydata =
header =
'' 'Height' 'Temperature'
'Level 1' '' ''
'Level 2' '' ''
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24. Import Excel data file xlsread('filename.xls')
Before using this command, you need to ensure that where the file is stored is in your search path (File  Set path)
If Excel is not installed on your computer, MATLAB cannot use xlsread or xlswrite
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25. xlswrite Exercise Write code L13E3.m:
Use xlswrite to create L13E3.xls for a table:
Use cell arrays
Sport Name \ Score
Wins
Loses
Ties
University Soccer 12 7 2
University Hockey 15 6 3
University Baseball 10 5 4
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26. Cell Array Assignment clear; clc c = cell(3,3); c{1,2} = 'string'
'r1 c1' 'r1 c2' 'r1 c3'
'r2 c1' 'r2 c2' []
'r3 c1' 'r3 c2' []
clear; clc
c = cell(3,3);
c{1,2} = 'string'
c(1,2) = {'string'} % same as above
c(1,:) = {'r1 c1', 'r1 c2', 'r1 c3'}
c{1,:} = {'r1 c1', 'r1 c2', 'r1 c3'} % wrong
c(2:3,1) = {'r2 c1', 'r3 c1'}
c(2:3,1) = {'r2 c1'; 'r3 c1'} % same as above
c(2:3,1:2) = {'r2 c1', 'r2 c2'; 'r3 c1','r3 c2'}
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27. Exercise Code % close file and clear workspace close; clear; clc;
% Assign the output file name
filename = 'L13E3.xls';
% Create a cell array to hold all header info
% -- First create a 4x4 empty cell array
head = cell(4,4);
% -- Then fill cells with row and column headers
head(1,:) = {'Sport Name \ Score', 'Wins', 'Loses','Ties'};
head(2:4,1) = {'University Soccer'; 'University Hockey'; 'University Baseball'};
% Define a matrix of 3 columns by 3 rows to hold the scores
score = [12,7,2; 15,6,3; 10,5,4];
% Write the headers to the Excel file
xlswrite (filename, head, 'Sheet1', 'A1');
% Write data to the Excel file
xlswrite (filename, score, 'Sheet1', 'B2');
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28. Summary I/O Interactive I/O with input Output with disp, fprintf
I/O to/from *.mat files with save and load
Writing to ASCII file with fprintf
Importing text with uiimport
Importing text with textscan
Importing text with urlread
Exporting to Excel file with xlswrite
Importing from Excel file with uiimport
Importing from Excel file with xlsread
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