Early File I/OTo help you get started with your final

project

1. Definition of “high level”2. Is using a High Level function appropriate?3. xlsread()4. xlswrite()5. dlmread()6. dlmwrite()

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1. Definition A file I/O function is considered HIGH-LEVEL if in ONE

SINGLE COMMAND, it 1. Opens the file2. Grabs the data3. Stores it in variables4. Closes the file

High-level functions can be used to:1. Load data from external sources (INPUT)2. Save data back to a file (OUTPUT)

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2. Wait.wait.wait… Before you decide if using a high level function is

possible, evaluate the following:

1. What type of file is it? (Excel, text, jpg..)

2. Find the organization overall (data in rows, or data in columns, data placed all over the place…)

3. Recognize the delimiters (space, tabs, new lines, -, :, / any specific symbol. What makes it obvious it is a new column? What makes it obvious it is a new row?)

4. Recognize the data types (all numerical? all strings? Or combination of both)

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2. Can High Level be used?

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2. Can High Level be used? cont.

“Neatly Organized”

1. Rows and Columns are “identifiable”

2. No “holes” anywhere3. Always the same patterns per

line4. There is no mixes of delimiters

(commas, spaces, tabs, dash.. )

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Questions Can these files be read using a high level function?

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Answers Can these files be read using a high level function?

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Yes Mixes of – and spaces.

Mixes of , and spaces. Yes. White space only.Decimals are ok.

The input files (.txt, .xls, .xlsx, .m) should all be in the same directory for function calls to work!

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2. Can High-Level be used?

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3. xlsread() F1, help. The most general form is:

Other calls possible:

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3. xlsread() F1, help. The most general form is:

Other calls possible:

11How do we work with all this?

Example: xlsread() Reading from a grade book %load data from file[values text raw] = xlsread('grades.xlsx');

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Test. See results!

Example: xlsread() Reading from a grade book %load data from file[values text raw] = xlsread('grades.xlsx');

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Test. See results!

Note that we are collecting multiple values using an array!

Results

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3. xlsread(), cont.

txt = 19 78 22 83 98 99 21 56 23 89 19 51

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nbs = 'Name' 'Age' 'Grade' 'Fred' '' '' 'joe' '' '' 'SaLLy' '' '' 'CharliE' '' '' 'mary' '' '' 'Ann' '' ''

raw = 'Name' 'Age' 'Grade' 'Fred' [ 19] [ 78] 'joe' [ 22] [ 83] 'SaLLy' [ 98] [ 99] 'CharliE' [ 21] [ 56] 'mary' [ 23] [ 89] 'Ann' [ 19] [ 51]

>> [txt nbs raw] = xlsread('grades.xlsx‘)

Variable names are up to the programmer. If named badly by mistake… BAD.

The order of the return values is important.

3. xlsread(), cont. Simply omit the 2nd and 3rd return value to collect only

numerical values.values = xlsread(‘grades.xlsx’);

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3. xlsread(), cont. Simply omit the 2nd and 3rd return value to collect only

numerical values.values = xlsread(‘grades.xlsx’);

If a project needs all the data together, collect the 1st and 2nd return values into a dummy variable.[trash trash data] = xlsread(‘grades.xlsx’);

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3. xlsread(), cont. Simply omit the 2nd and 3rd return value to collect only

numerical values.values = xlsread(‘grades.xlsx’);

If a project needs all the data together, collect the 1st and 2nd return values into a dummy variable.[trash trash data] = xlsread(‘grades.xlsx’);

If there happen to be ‘holes’ in the spreadsheet, MATLAB fills it with a NaN value (not a number). The function isnan() can help determine where those ‘holes’ are.

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3. xlsread(), cont.

This function will not work under Citrix, since Excel is not installed on Citrix. Come to the lab to do labs and homework.

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4. xlswrite() Arrays can also be written to excel sheets:

xlswrite(<filename>, <array>, <sheet>, <range>)

The <sheet> and <range> arguments are optional.

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clcclear %create phony datatable = rand(5,3)*100; %print to excelxlswrite('testingTesting.xls',table)

2. Can High-Level be used?

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NUMBERS ONLY.

5. Using Delimiters Rows are delimited by the new line character (enter key,

invisible to the human eye).

Columns are delimited by the same delimiter each time: Default delimiters: commas, and white space Other delimiters: any other symbol : - /

F1 = help

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5. Using Delimiters, cont. Delimiter: white space (spaces, or tabs)

23Missing data is filled by zeros.

5. Using Delimiters, cont. Delimiter: commas Added feasibility to ‘skip’ columns

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5. Using Delimiters, cont. Delimiter: other than the defaults

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Specify the delimiter as the 2nd argument.

5. Using Delimiters, cont. Delimiter: other than the defaults

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Specify the delimiter as the 2nd argument.

5. Using Delimiters, cont. "Neatly Organized" is important.

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BAD RESULTS.Two delimiters (spaces and colons) in the file. Matlab is lost.

dlmwrite()M = [2, 123; 87, 4];dlmwrite('test.txt', M, ',');

File contains:2,12387,4

EXCEPT…

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dlmwrite()By default, dlmwrite() saves files using Unix line endings – so if

you look at the file in Notepad:

This is not “wrong” – just different. This can be changed by setting the “newline” attribute when you call the function:

dlmwrite('test.txt', M, ',', 'newline', 'pc');

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