Lecture 22:
Reading and writing text files gerasoulis 1

Overview
• Reading Data from a file.
• Reading fixed format table-like data.
• Writing Data to a string
• Writing data to a file gerasoulis 2

Reading a text file into a cell array
• Large amounts of text data can be stored in
“plain text” or “plain ascii” files, with a .txt
extension, e.g. mobydick.txt
• ========mobydick.txt=======
Call me Ishmael. Some years ago – never mind how long precisely – having little or no money in my purse, and nothing particular to interest me on shore,
I thought I would sail about a little and see the watery part of the world.
It is a way I have of driving off the spleen and regulating the circulation.
gerasoulis 3

Reading text files
• lines = textread( 'mobydick.txt' , '%s' ,
'delimiter' , '\n' );
• Successive lines of a text file can be read into the cells of a cell array using the textread function.
• '%s' , = reading a string ,
• 'delimiter' , '\n'= reading until the end of line.
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Cell array
• Textread creates a cell array or an array
• In the previous example lines is a cell array.
• lines{3,1}=
I thought I would sail about a little and see the watery part of the world.
>> size(lines)
• ans =
6 1 gerasoulis 5

Changing Delimiter
• Delimiter could be a period, a comma a letter etc.
• What will the following do?
• lines = textread( 'mobydick.txt' , '%s' ,
'delimiter' , '.' );
• lines = textread( 'mobydick.txt' , '%s' ,
'delimiter' , ' ' ); gerasoulis 6

Reading formatted data
• Suppose we have a text file elements.txt that contains a combination of numerical data and strings, in a fixed format.
• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8 hydrogen helium lithium beryllium boron carbon nitrogen oxygen
• 9 fluorine
• 10 neon
H 1.01
He 4.00
Li 6.94
Be 9.01
B 10.81
C 12.01
N 14.01
O
F
16.00
19.00
Ne 20.18
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Elements.txt
The first column is integers, second strings, third strings and fourth real(float).
• format :
• %u integer
• %s string
• %f float
• textread( 'elements.txt' , ʻ %u %s %s %f ' ); gerasoulis 8

Elements.txt
• We can read each column into a vectors of same type elements.
• [atomNums names symbols masses] = ...
textread( 'elements.txt' , '%u %s %s %f' );
• See readTable.m
• Tab={atomNums names symbols masses}
Will generate a cell array Tab of the table that can be passed as a single argument.
See byName.m
gerasoulis 9

atomNums names symbols masses atomNums =
1
2
3
4
5
6
7
8
9
10 names =
'hydrogen'
'helium'
'lithium'
'beryllium'
'boron'
'carbon'
'nitrogen'
'oxygen'
'fluorine'
'neon' symbols =
'H'
'He'
'Li'
'Be'
'B'
'C'
'N'
'O'
'F'
'Ne' masses =
1.0100
4.0000
6.9400
9.0100
10.8100
12.0100
14.0100
16.0000
19.0000
20.1800
gerasoulis 10

For more textread details:
• >>>help textread
• TEXTREAD Read formatted data from text file.
• A = TEXTREAD('FILENAME')
• A = TEXTREAD('FILENAME','',N)
• A =
TEXTREAD('FILENAME','',param,value,
...) gerasoulis 11

For more textread details:
• Supported conversion specifications:
• %n - read a number - float or integer (returns double array)
• %5n reads up to 5 digits or until next delimiter
• %d - read a signed integer value (returns double array)
• %5d reads up to 5 digits or until next delimiter
• %u - read an integer value (returns double array)
• %5u reads up to 5 digits or until next delimiter
• %f - read a floating point value (returns double array)
• %5f reads up to 5 digits or until next delimiter
• %s - read a whitespace separated string (returns cellstr)
• %5s reads up to 5 characters or until whitespace
• %q - read a double-quoted string, ignoring the quotes (returns cellstr)
• %5q reads up to 5 non-quote characters or until whitespace
• %c - read character or whitespace (returns char array)
• %5c reads up to 5 characters including whitespace
• ….
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Printing data to A STRINGsprintf
• STR = SPRINTF(FORMAT, A, ...)
• applies the FORMAT to all elements of array A and any additional array arguments in column order, and returns the results to string STR.
• str=sprintf('%15.5f',1/eps) str= 4503599627370496.00000
• sprintf('%s','hello')
hello gerasoulis 13

sprintf
• A=[1 2 3]
• >> sprintf(' %f ',A)
• 1.000000 2.000000 3.000000
• Notice the blank spaces in the format.
• Without blank spaces it will print as follows
• >> sprintf('%f',A)
1.0000002.0000003.000000
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sprintf
• sprintf(' %u ',A)
• ans =
1 2 3
• sprintf('%d',A)
• ans =
123
• sprintf( '%5d',A) ==?????
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Printing column vectors
• Assume now that we have a column vector—Notice that sprintf prints the elements as row vector--PRINTING S A
STRING a ROW-WISE OPERATION !
• B=[1
2
3] sprintf('%5d',B) ans =
1 2 3 gerasoulis 16

Sprintf
• If we want to use sprintf to print elements column-wise then we need to print each element at a time!
• sprintf('%5d',B(1))
• ans =
1
• >> sprintf('%5d',B(2))
• ans =
2 gerasoulis 17

Printing Column-wise with sprintf
• >> for i=1:3 st(i,:)=sprintf('%5d',B(i)); end
• st =
1
2
3 gerasoulis 18

Writing on files
• Instead of writing the results on a variable or on the matlab screen we can also
WRITE the results on file. We can do this as follows:
• First open a file.txt
• fid = fopen( ʻ file.txt', 'w');
• fid====File ID
• w===Write
• file.txt===File name gerasoulis 19

Writing on files-fprintf
• fprintf(fid,'%5d',A)
• This command will write on the file with fid the vector A row-wise.
File.txt 1 2 3
• To STOP writing on this file you must
CLOSE it using
• fclose(fid)
See printTable.m
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Example with \n = next line gerasoulis 21

Example with \n = next line
• fid = fopen('results.txt', 'w');
• fprintf(fid, 'experimental results:');
• fprintf(fid, '\nxdata: ');
• fprintf(fid, '%6.2f', xdata);
• fprintf(fid, '\nydata: ');
• fprintf(fid, '%6.2f', ydata);
• fprintf(fid, '\nresults: ');
• fprintf(fid, '%6.2f', results);
• fclose(fid); gerasoulis 22

Writing files with literal strings gerasoulis 23

Writing files with literal strings gerasoulis 24

Writing files with literal strings
• fid = fopen('cs112.txt', 'w');
• fprintf(fid, 'data for CS112 assignment work
\nSpring 2007 \n\n');
• for i = 1:length(data)
• fprintf(fid, '%s\nused drop-in %u times\naverage assignment time %3.1f
hours\nassignment grade %4.1f\n\n', data{i}{1}, data{i}{2}, data{i}{3}, data{i}{4});
• end
• fclose(fid); gerasoulis 25

Reading an Excel File-xlsread
• We can also read excel spreadsheet into
Matlab cell arrays.
• [NUMERIC,TXT,RAW]=XLSREAD(FILE)
• NUMERIC= is the numerical part of the excel file.
• TXT= is the text part
• RAW= is the entire excel file in RAW format gerasoulis 26

gerasoulis 27

[NUMERIC,TXT,RAW]=XLSRE
AD('Book1.xlsx')
• TXT =
TXT
• Columns 1 through 5
• 'Date' 'Time' 'Open' 'High' 'Low'
• '10/24/2005' '' '' '' ''
• '10/25/2005' '' '' '' ''
• '10/26/2005' '' '' '' ''
• '10/27/2005' '' '' '' ''
• '10/28/2005' '' '' '' ''
• '10/31/2005' '' '' '' ''
• '11/1/2005' '' '' '' ''
• '11/2/2005' '' '' '' ''
• '11/3/2005' '' '' '' ''
• '11/4/2005' '' '' '' ''
• '11/7/2005' '' '' '' ''
• '11/8/2005' '' '' '' '' gerasoulis 28

RAW
• RAW =
• Columns 1 through 4
• 'Date' 'Time' 'Open' 'High'
• '10/24/2005' [0.3958] [55.2500] [56.7900]
• '10/25/2005' [0.3958] [56.4000] [56.8500]
• '10/26/2005' [0.3958] [56.2800] [57.5600]
• '10/27/2005' [0.3958] [56.9900] [57.0100]
• '10/28/2005' [0.3958] [56.0400] [56.4300]
• '10/31/2005' [0.3958] [55.2000] [57.9800]
• '11/1/2005' [0.3958] [57.2400] [58.1400]
• '11/2/2005' [0.3958] [57.7200] [ 60]
• '11/3/2005' [0.3958] [60.2600] [62.3200]
• '11/4/2005' [0.3958] [60.3500] [61.2400]
• '11/7/2005' [0.3958] [60.8500] [61.6700]
• '11/8/2005' [0.3958] [59.9500] [60.3800
]
29

RAW
• Columns 5 through 7
• 'Low' 'Close' 'Volume'
• [55.0900] [56.7900] [21884143]
• [55.6900] [56.1000] [16655439]
• [55.9200] [57.0300] [22608343]
• [55.4100] [55.4100] [15044140]
• [54.1700] [54.4700] [27503152]
• [54.7500] [57.5900] [33727255]
• [56.8700] [57.5000] [26837071]
• [57.6000] [59.9500] [30857901]
• [60.0700] [61.8499] [31585059]
• [59.6200] [61.1500] [31368909]
• [60.1400] [60.2300] [22815383]
• [59.1000] [59.9000] [16920183] gerasoulis 30