file i/o high-level functions 1. definition 2. is a high-level function appropriate? 3. xlsread() 4....
TRANSCRIPT
File I/OHigh-Level Functions
1. Definition
2. Is a High-Level function appropriate?
3. xlsread()4. dlmread()
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
5
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.. )
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.
Whatever you do, the input files (.txt, .xls, .xlsx, .m) should all be in the same directory for function calls to work!
8
10
3. xlsread()
F1, help. The most general form is:
Other calls possible:
11
3. xlsread()
F1, help. The most general form is:
Other calls possible:
How do we work with all this?
Example: xlsread()
Name who has the highest grade! %load data from file[values text raw] = xlsread('grades.xlsx');
%find the position of the maximum grade
%find whose name is associated with that position
12
Test. See results!
14
Results
To find the highest grade, work on the array values.
To find the name, either use text or raw!
Example: xlsread()
Name who has the highest grade! %load data from file[values text raw] = xlsread('grades.xlsx');
%find the position of the maximum grade[trash row]= max(values(:,2));
%find whose name is associated with that positionname = text{row+1,1}; %+1 due to headersfprintf('%s got the highest grade\n', name)
15
Example: xlsread()
Name who has the highest grade! %load data from file[values text raw] = xlsread('grades.xlsx');
%find the position of the maximum grade[trash row]= max(values(:,2));
%find whose name is associated with that positionname = text{row+1,1}; %+1 due to headersfprintf('%s got the highest grade\n', name)
16
3. xlsread(), cont.
txt = 19 78 22 83 98 99 21 56 23 89 19 51
17
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’);
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 happens 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(<filename>, <array>, <sheet>, <range>)
The <sheet> and <range> arguments are optional.
20
clcclear %create phony datatable = rand(5,3)*100; %print to excelxlswrite('testingTesting.xls',table)
2. Can High-Level be used?
21
NUMBERS ONLY.
22
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
23
5. Using Delimiters, cont.
Delimiter: white space (spaces, or tabs)
Missing data is filled by zeros.
24
5. Using Delimiters, cont.
Delimiter: commas Added feasibility to ‘skip’ columns
25
5. Using Delimiters, cont.
Delimiter: other than the defaults
Specify the delimiter as the 2nd argument.
26
5. Using Delimiters, cont.
Delimiter: other than the defaults
Specify the delimiter as the 2nd argument.
27
5. Using Delimiters, cont.
"Neatly Organized" is important.
BAD RESULTS.Two delimiters (spaces and colons) in the file. Matlab is lost.
Wrapping Up
One command opens, loads, and closes the file.
Before anything, look in the file, and decide whether a high-level function is appropriate
xlsread(), dlmread() are common. There are many other high-level functions.
The variables are automatically created by MATLAB. Sometimes as regular array [ ] Other times as cell array { }
Use knowledge from previous chapter to analyze the data in the arrays. FOR loops, A(position), A(row,col), A{row,col},
max(arrayName), mean(arrayName), sort(..), slicing, deleting, augmenting…
28