Early File I/O To 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() 1

1. Definition A file I/O function is considered HIGH-LEVEL if in ONE SINGLE COMMAND, it 1. Opens the file 2. Grabs the data 3. Stores it in variables 4. 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) 2

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) 3

2. Can High Level be used? 4

2. Can High Level be used? cont. “Neatly Organized” 1. Rows and Columns are “identifiable” 2. No “holes” anywhere 3. Always the same patterns per line 4. There is no mixes of delimiters (commas, spaces, tabs, dash.. ) 5

Questions Can these files be read using a high level function? 6

Answers Can these files be read using a high level function? 7 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! 8

2. Can High-Level be used? 9

3. xlsread() F1, help. The most general form is: Other calls possible: 10

3. xlsread() F1, help. The most general form is: Other calls possible: 11 How do we work with all this?

Example: xlsread() Reading from a grade book %load data from file [values text raw] = xlsread('grades.xlsx'); 12 Test. See results!

Example: xlsread() Reading from a grade book %load data from file [values text raw] = xlsread('grades.xlsx'); 13 Test. See results! Note that we are collecting multiple values using an array!

Results 14

3. xlsread(), cont. txt = 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 2 nd and 3 rd return value to collect only numerical values. values = xlsread(‘grades.xlsx’); 16

3. xlsread(), cont. Simply omit the 2 nd and 3 rd return value to collect only numerical values. values = xlsread(‘grades.xlsx’); If a project needs all the data together, collect the 1 st and 2 nd return values into a dummy variable. [trash trash data] = xlsread(‘grades.xlsx’); 17

3. xlsread(), cont. Simply omit the 2 nd and 3 rd return value to collect only numerical values. values = xlsread(‘grades.xlsx’); If a project needs all the data together, collect the 1 st and 2 nd 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. 18

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. 19 

4. xlswrite() Arrays can also be written to excel sheets: xlswrite(,,, ) The and arguments are optional. 20 clc clear %create phony data table = rand(5,3)*100; %print to excel xlswrite('testingTesting.xls',table)

2. Can High-Level be used? 21 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 22

5. Using Delimiters, cont. Delimiter: white space (spaces, or tabs) 23 Missing data is filled by zeros.

5. Using Delimiters, cont. Delimiter: commas Added feasibility to ‘skip’ columns 24

5. Using Delimiters, cont. Delimiter: other than the defaults 25 Specify the delimiter as the 2 nd argument.

5. Using Delimiters, cont. Delimiter: other than the defaults 26 Specify the delimiter as the 2 nd argument.

5. Using Delimiters, cont. "Neatly Organized" is important. 27 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: 2,123 87,4 EXCEPT… 28

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'); 29