This is simply a blog containing small code snippets I found useful during my work!
giovedì 19 giugno 2014
Dale Carnegie
I have just read a very interesting book:
"How to Win Friends and Influence People" of Dale Carnegie.
I have to say it is a great book! I have been really hit very hard inside.
Nice part of this book is that it has a very short sentence with a great recap power.
I am currently reading another of his book: "How to stop worring and start living".
I am posting now his "Golden Rules" in order to have a quick reference:
Become a Friendlier Person
1. Don’t criticize, condemn or complain.
2. Give honest, sincere appreciation.
3. Arouse in the other person an eager want.
4. Become genuinely interested in other people.
5. Smile.
6. Remember that a person’s name is to that person the sweetest and most important sound in any language.
7. Be a good listener. Encourage others to talk about themselves.
8. Talk in terms of the other person’s interests.
9. Make the other person feel important - and do it sincerely.
Win People to Your Way of Thinking
10. The only way to get the best of an argument is to avoid it.
11. Show respect for the other person’s opinion. Never say, “You’re wrong.”
12. If you are wrong, admit it quickly and emphatically.
13. Begin in a friendly way.
14. Get the other person saying “yes, yes” immediately.
15. Let the other person do a great deal of the talking.
16. Let the other person feel that the idea is his or hers.
17. Try honestly to see things from the other person’s point of view.
18. Be sympathetic with the other person’s ideas and desires.
19. Appeal to the nobler motives.
20. Dramatize your ideas.
21. Throw down a challenge.
Be a Leader
22. Begin with praise and honest appreciation.
23. Call attention to people’s mistakes indirectly.
24. Talk about your own mistakes before criticizing the other person.
25. Ask questions instead of giving direct orders.
26. Let the other person save face.
27. Praise the slightest improvement and praise every improvement. Be “hearty in your
approbation and lavish in your praise.”
28. Give the other person a fine reputation to live up to.
29. Use encouragement. Make the fault seem easy to correct.
30. Make the other person happy about doing the thing you suggest
Fundamental Principles for Overcoming Worry
1. Live in “day tight compartments.”
2. How to face trouble:
a. Ask yourself, “What is the worst that can possibly happen?”
b. Prepare to accept the worst.
c. Try to improve on the worst.
3. Remind yourself of the exorbitant price you can pay for worry in terms of your health.
Basic Techniques in Analyzing Worry
1. Get all the facts.
2. Weigh all the facts — then come to a decision.
3. Once a decision is reached, act!
4. Write out and answer the following questions:
a. What is the problem?
b. What are the causes of the problem?
c. What are the possible solutions?
d. What is the best possible solution?
Break the Worry Habit Before It Breaks You
1. Keep busy.
2. Don’t fuss about trifles.
3. Use the law of averages to outlaw your worries.
4. Cooperate with the inevitable.
5. Decide just how much anxiety a thing may be worth and refuse to give it more.
6. Don’t worry about the past.
Cultivate a Mental Attitude that will Bring You Peace and Happiness
1. Fill your mind with thoughts of peace, courage, health and hope.
2. Never try to get even with your enemies.
3. Expect ingratitude.
4. Count your blessings — not your troubles.
5. Do not imitate others.
6. Try to profit from your losses.
7. Create happiness for others.
domenica 27 aprile 2014
Basic SQL Operation in R
I want to have in R the equivalent of most of the basic operations normally performed in SQL.
In this post it will follow a sniplet in SQL and immediately after the correspondent in R.
Topics Covered:
- Distinct
- Where
- Inner / outer joins
- Group by
Before starting with the Pure R syntax, just keep in mind that R is providing a very useful package called SQLDF. Through this package it is possible to perform a simple SQL query over tables / data frames.
# installs everything you need to use sqldf with SQLite
# including SQLite itself
install.packages("sqldf")
# shows built in data frames
data()
# load sqldf into workspace
library(sqldf)
sqldf("select * from iris limit 5")
sqldf("select count(*) from iris")
sqldf("select Species, count(*) from iris group by Species")
# create a data frame
DF <- data.frame(a = 1:5, b = letters[1:5])
sqldf("select * from DF")
sqldf("select avg(a) mean, variance(a) var from DF") # see example 15
Source: http://code.google.com/p/sqldf/
WHERE
SELECT *
FROM df1
WHERE product = "Toaster"
In R:
df1 = data.frame(CustomerId=c(1:6),Product=c(rep("Toaster",3),rep("Radio",3))) ;
df <- df1[df1$Product=="Toaster",];
DISTINCT
the select distinct in SQL: select distinct x
from my_table;
The equivalent in R is:
> x <- list(a=c(1,2,3), b = c(2,3,4), c=c(4,5,6))
> xx <- unlist(x)
> xx
a1 a2 a3 b1 b2 b3 c1 c2 c3
1 2 3 2 3 4 4 5 6
> unique(xx)
[1] 1 2 3 4 5 6
INNER / OUTER JOINS
Having in SQL the following query: select *
from product [left] [right] [outer] join countries
on (product.customer_id = countries.customer_id)
In R:
df1 = data.frame(CustomerId=c(1:6),Product=c(rep("Toaster",3),rep("Radio",3)))
df2 = data.frame(CustomerId=c(2,4,6),State=c(rep("Alabama",2),rep("Ohio",1)))
> df1
CustomerId Product
1 Toaster
2 Toaster
3 Toaster
4 Radio
5 Radio
6 Radio
> df2
CustomerId State
2 Alabama
4 Alabama
6 Ohio
#Outer join:
merge(x = df1, y = df2, by = "CustomerId", all = TRUE)
#Left outer:
merge(x = df1, y = df2, by = "CustomerId", all.x=TRUE)
#Right outer:
merge(x = df1, y = df2, by = "CustomerId", all.y=TRUE)
#Cross join:
merge(x = df1, y = df2, by = NULL)
Source:
http://stackoverflow.com/questions/1299871/how-to-join-data-frames-in-r-inner-outer-left-right
GROUP BY
For the Group By function there are many options.
Let's start with the most basic one:
Having in SQL the following snipplet:
CREATE TABLE my_table (
a varchar2(10 char),
b varchar2(10 char),
c number
);
SELECT a, b, mean(c)
FROM my_table
GROUP BY a, b
In R:
grouped_data <- aggregate(my_table, by=list(my_table$a, my_table$b, FUN=mean);
Alternatively:
> mydf
A B
1 1 2
2 1 3
3 2 3
4 3 5
5 3 6
> aggregate(B ~ A, mydf, sum)
A B
1 1 5
2 2 3
3 3 11
If your data are large, I would also recommend looking into the "data.table" package.
> library(data.table)
> DT <- data.table(mydf)
> DT[, sum(B), by = A]
A V1
1: 1 5
2: 2 3
3: 3 11
And finally the most recommended ddply function:
> DF <- data.frame(A = c("1", "1", "2", "3", "3"), B = c(2, 3, 3, 5, 6))
> library(plyr)
> DF.sum <- ddply(DF, c("A"), summarize, B = sum(B))
> DF.sum
A B
1 1 5
2 2 3
3 3 11
Source:
http://stackoverflow.com/questions/18799901/data-frame-group-by-column
venerdì 25 aprile 2014
Boss Vs. Leader
I think it is a bit old, but I would like to have it stamped it on my blog...
I do not have so much time these days :/ this is the most I can do...
I do not have so much time these days :/ this is the most I can do...
domenica 13 aprile 2014
ORACLE: Analytical Functions
The concept of analytical query is something that can highly speed up the development and the execution of your queries.
In particular because they are automatically optimized by oracle itself.
Here there are reported in a veeeeery small nutshell:
Count (member of elements in the same group)
SELECT empno, deptno, COUNT(*) OVER (PARTITION BY deptno) DEPT_COUNT FROM emp WHERE deptno IN (20, 30); EMPNO DEPTNO DEPT_COUNT ---------- ---------- ---------- 7369 20 5 7566 20 5 7788 20 5 7902 20 5 7876 20 5 7499 30 6 7900 30 6 7844 30 6 7698 30 6 7654 30 6 7521 30 6 11 rows selected.
Row Number (id of the entry within the group)
SELECT empno, deptno, hiredate, ROW_NUMBER( ) OVER (PARTITION BY deptno ORDER BY hiredate NULLS LAST) SRLNO FROM emp WHERE deptno IN (10, 20) ORDER BY deptno, SRLNO; EMPNO DEPTNO HIREDATE SRLNO ------ ------- --------- ---------- 7782 10 09-JUN-81 1 7839 10 17-NOV-81 2 7934 10 23-JAN-82 3 7369 20 17-DEC-80 1 7566 20 02-APR-81 2 7902 20 03-DEC-81 3 7788 20 09-DEC-82 4 7876 20 12-JAN-83 5 8 rows selected.
Rank & Dense Rank (member of elements in the same group)
SELECT empno, deptno, sal, RANK() OVER (PARTITION BY deptno ORDER BY sal DESC NULLS LAST) RANK, DENSE_RANK() OVER (PARTITION BY deptno ORDER BY sal DESC NULLS LAST) DENSE_RANK FROM emp WHERE deptno IN (10, 20) ORDER BY 2, RANK; EMPNO DEPTNO SAL RANK DENSE_RANK ------ ------- ----- ----- ---------- 7839 10 5000 1 1 7782 10 2450 2 2 7934 10 1300 3 3 7788 20 3000 1 1 7902 20 3000 1 1 7566 20 2975 3 2 7876 20 1100 4 3 7369 20 800 5 4 8 rows selected.
Lead & Lag (next / previous member of the group respect the current element)
SELECT deptno, empno, sal, LEAD(sal, 1, 0) OVER (PARTITION BY dept ORDER BY sal DESC NULLS LAST) NEXT_LOWER_SAL, LAG(sal, 1, 0) OVER (PARTITION BY dept ORDER BY sal DESC NULLS LAST) PREV_HIGHER_SAL FROM emp WHERE deptno IN (10, 20) ORDER BY deptno, sal DESC; DEPTNO EMPNO SAL NEXT_LOWER_SAL PREV_HIGHER_SAL ------- ------ ----- -------------- --------------- 10 7839 5000 2450 0 10 7782 2450 1300 5000 10 7934 1300 0 2450 20 7788 3000 3000 0 20 7902 3000 2975 3000 20 7566 2975 1100 3000 20 7876 1100 800 2975 20 7369 800 0 1100 8 rows selected.
First Value & Last Value
-- How many days after the first hire of each department were the next -- employees hired? SELECT empno, deptno, hiredate ? FIRST_VALUE(hiredate) OVER (PARTITION BY deptno ORDER BY hiredate) DAY_GAP FROM emp WHERE deptno IN (20, 30) ORDER BY deptno, DAY_GAP; EMPNO DEPTNO DAY_GAP ---------- ---------- ---------- 7369 20 0 7566 20 106 7902 20 351 7788 20 722 7876 20 756 7499 30 0 7521 30 2 7698 30 70 7844 30 200 7654 30 220 7900 30 286 11 rows selected.
Source:
http://www.orafaq.com/node/55
mercoledì 9 aprile 2014
File system access on Oracle
It may sound easy, but accessing the file system from oracle can be painful.
I am not talking about read / write a file. I am talking about making a ls or dir command, crete folders, move files, etc.
In this post I would like to recall an easy system about making ls.
Actually the solution is already very well explained in this web page:
http://plsqlexecoscomm.sourceforge.net/
The solution is mainly based on a java package installed in the Oracle DB, which is accessing the file system and arranging the data in a proper way.
First of all it is needed to install the package (available on the link above) and then perform a simple query like the one below:
select *
from table(
file_pkg.get_file_list(file_pkg.get_file('/'))
)
And here you are: you get the result of a ls command executed on the root accessible as a simple select.
domenica 30 marzo 2014
SAP HANA: exception Handling
I invest a bit of time in order to understand how does it exactly works.
I prepared a small tutorial and summerized here below.
Theory:
In java
public class myClass() {
...
public void myMethod() {
...
try {
//code to be executed causing exception
}
catch(Exception e) {
//log the exception
}
...
}
...
}
Equivalent in SQLScript
CREATE PROCEDURE myproc AS
BEGIN
...
DECLARE EXIT HANDLER FOR SQL_ERROR_CODE MY_SQL_ERROR_CODE
BEGIN
-- log the exception
END;
-- code to be executed causing exception
end;
Practical example
copy and paste on SAP HANA Studio. First prepare something:
CREATE TABLE MYTAB (I INTEGER PRIMARY KEY);
drop PROCEDURE myproc;
Then create this procedure:
CREATE PROCEDURE myproc AS
BEGIN
declare myvar int;
DECLARE EXIT HANDLER FOR SQL_ERROR_CODE 1299
BEGIN
write_debug_log('MARCO TEST',
'Handler of the NO_DATA_FOUND exception of the select below (after the following begin end block)',
'SQL_ERROR_CODE = ' || ::SQL_ERROR_CODE || '; SQL_ERROR_MESSAGE = ' || ::SQL_ERROR_MESSAGE);
END;
begin
declare my_test int;
--CASE GENERIC FOR ANY POSSIBLE EXCEPTION
DECLARE EXIT HANDLER FOR SQLEXCEPTION
begin
write_debug_log('MARCO TEST',
'separate handler for division by 0',
'SQL_ERROR_CODE = ' || ::SQL_ERROR_CODE || '; SQL_ERROR_MESSAGE = ' || ::SQL_ERROR_MESSAGE);
end;
my_test := 1/0;
end;
SELECT I INTO myVar FROM MYTAB; --NO_DATA_FOUND exception
SELECT 'NeverReached_noContinueOnErrorSemantics' FROM DUMMY;
END;
Please, notice that I am using my classing logging procedure.
Just substitute this procedure with any other suitable to your environment for logging...
Then let it run:
--execute the code and raise the exceptions
call myproc;
--check the situation in the log table
select * from log
order by id desc;
Again, here is the code for accessing my log table...
Just use the one of your environment.
Just use the one of your environment.
sabato 15 marzo 2014
Octave Cheat Sheet
Octave Cheat Sheet:
I found this very interesting cheat sheet about Octave here:
Source http://altons.github.io/octave/2013/05/05/octave-commands-cheat-sheet/
I think it is very great, but there are couple of commands missing (like PS1, which in my opinion makes your life better!).
So I have taken it and extendend with some commands.
I found this very interesting cheat sheet about Octave here:
Source http://altons.github.io/octave/2013/05/05/octave-commands-cheat-sheet/
I think it is very great, but there are couple of commands missing (like PS1, which in my opinion makes your life better!).
So I have taken it and extendend with some commands.
Management & Help
Task
|
Command
|
exits software
|
quit or exit
|
list variables in session
|
who
|
list variables in session with info about type
|
whos
|
deallocate variable(s)
|
clear varname
|
displays search path
|
path
|
Adds path to search
|
addpath
|
clear screen
|
clc
|
list .m files in dir
|
what
|
search for keyword
|
lookfor
|
displays help for function
|
help funname
|
Parse and execute the contents of FILE
|
source(".octaverc")
|
List installed packages
|
pkg list
|
Install packages
|
pkg install [-auto or -noauto] pkg_name.tar.gz
|
Describe packages
|
pkg describe pkg_name
|
Load/Unload package
|
pkg load/unload pkg_name
|
Uninstall package
|
pkg uninstall pkg_name
|
Shell Commands
Task
|
Command
|
Change Linde starter
|
PS1(‘desired Starter’); %PS1(‘>> ‘);
|
change working directory to dir
|
cd dirname
|
print working directory
|
Pwd
|
print directory listing
|
ls
|
return value of named environment variable
|
getenv (string)
|
execute arbitrary shell command string
|
system (cmd)
|
Load the file
You will load a file and make it available with a
Varible having same name of the file without extension
|
Load FILENAME_IN_PWD
Load(‘FILENAME_IN_PWD’);
|
Save variable into file
You will load a file and make it available with a
Varible having same name of the file without extension
|
save FILENAME_IN_PWD
VARIABLE_NAME;
|
Special Operators
Definition
|
Operator
|
Example
|
comment
|
%
|
% Initialising
|
wildcard
|
*
|
clear p*
|
array
|
[ ]
|
[1 2; 3 4]
|
Cell Arrays
|
{ }
|
p = { 10 , 15 , "rectangle" }; p{1} =10
|
ranges
|
start:step:stop (default step=1)
|
1:10 or 1:10:100
|
variable assignment
|
=
|
A=magic(3);
|
do not display
|
;
|
a=1;
|
Workflow
Task
|
Command
|
Suspend the execution of the program.
|
pause; or pause(5)
|
print string to the stout
|
fprintf("Hello World")
|
Vectors & Matrices
Rules
· Square brackets delimit literal matrices.
· Commas separate elements on the same row.
· Semicolons separate rows.
· Commas may be replaced by spaces, and
· semicolons may be replaced by one or more newlines.
· Elements of a matrix may be arbitrary expressions, provided that all the dimensions agree.
· Optional: Matrices are denoted by uppercase letters A,B,X etc while vectors by lowercase letters a,b,y etc.
· Commas separate elements on the same row.
· Semicolons separate rows.
· Commas may be replaced by spaces, and
· semicolons may be replaced by one or more newlines.
· Elements of a matrix may be arbitrary expressions, provided that all the dimensions agree.
· Optional: Matrices are denoted by uppercase letters A,B,X etc while vectors by lowercase letters a,b,y etc.
Example
|
Expression
|
enter a row vector
|
[ x, y, ... ]
|
enter a column vector
|
[ x; y; ... ]
|
enter a 2×2 matrix
|
[ w, x; y, z ]
|
Return a row vector with N linearly spaced elements between BASE and
LIMIT
|
linspace (BASE, LIMIT, N)
|
Similar to linspace except that the values are logarithmically
spaced
|
logspace(BASE, LIMIT, N)
|
Higher Dimensional Arrays
|
B(z,y,z)=1
|
Sorting arrays
|
sort(A); or sort(A, 'descend');
|
Return true if any element in array is non-zero
|
any(A)
|
Return true if all element are non-zero
|
all(A)
|
Return a vector of indices of a matrix
|
[i , j] = find(A<0.5)
|
Array Operations
Task
|
Function
|
select elements of a vector
|
A(i)
|
select elements of a matrix
|
A(i,j)
|
select rows (columns) corresponding to the elements of a range
|
A(1:2,1); A(1:2,1:5);
|
select all rows (columns)
|
A(:,1); A(3,:);
|
Delete a row/column of a matrix
|
A(2,:)= [] or A(:,5) = []
|
Linear Algebra
Task
|
Function
|
dimensions of the array
|
size
|
returns larger dimension
|
length
|
allocates array with 0’s
|
zeros
|
allocates array with 1’s
|
ones
|
transpose array
|
'
|
Compute the determinant of A.
|
det(A)
|
inverse of matrix
|
inv
|
pseudo inverse of matrix
|
pinv
|
Calculate Eigenvalues / Eigenvectors of matrix A
|
eig(A) or [V,L] = eig(A)
|
Identity matrix
|
eye
|
Compute the rank of a Matrix
|
rank(A)
|
returns the lower triangular part of A
|
tril(A)
|
returns the upper triangular part of A
|
triu(A)
|
Create an N-by-N magic square
|
magic
|
Compute the dot product of two vectors
|
dot(A,B)
|
Compute the vector cross product of two 3-dimensional vectors X and Y
|
cross(X,Y)
|
interval range arrays
|
v = 1:0.1:2
%vector = STARTING_AT:DELTA:ENDING_AT
|
Plotting
Task
|
Command
|
Example
|
2-D plot
|
plot
|
plot(x,y); plot(x, a+b+c);
|
Surface plot
|
surf
|
surf(theta0, theta1, J);
|
Contour plot
|
contour
|
contour(theta0, theta1, J, logspace(-2, 3, 20))
|
Specify x-, y-, or z-axis labels for the current axis
|
[x,y,z]label
|
xlabel('k lags')
|
Set a plot window to plot window N
|
figure
|
figure;plot(x, a);
|
close figure window(s)
|
close
|
close [***(N),all,all hidden***]
|
new graphic objects are added to the plot
|
hold
|
hold on;plot(x, b);
|
Clear plot and restore default graphics settings
|
hold
|
hold off;
|
Display a legend for the axes
|
legend
|
plot(X,Y);legend('Temperature', 'Gas Demand');
|
give a title
|
title
|
title('myTitle');
|
export the chart
|
print
|
Print –dpng ‘filename.png’
|
Math Functions
Type
|
Function
|
Examples
|
Sum of elements along dimension DIM
|
sum
|
sum([1 2 3 4])
|
Product of elements along dimension DIM
|
prod
|
prod([1 2 3 4)]
|
Trigonometric
|
sin, cos, tan
|
floor((1+tan(1.2)) / 1.2)
|
Inverse Trigonometric
|
asin, acos, atan
|
|
Natural Logarithm
|
log
|
|
Base 10 Logarithm
|
log10
|
log10(100)/log10(10)
|
Exponentiation
|
exp
|
exp(0)
|
Absolute value
|
abs
|
abs(-3)
|
Square Root
|
sqrt
|
sqrt(3^2 + 4^2)
|
X raised to the Y power
|
power(X,Y)
|
power(3,2)
|
Real part of complex number
|
real
|
real(3+5I)
|
Imaginary part of complex number
|
imag
|
imag(3+5I)
|
Evaluate polynomials
|
polyval
|
polyval([2 10.1 0 6],0)
|
Write formatted polynomial
|
polyout
|
polyout([2 -3 1],"x")
|
Return the largest integer not greater than X
|
floor
|
floor(1.9)
|
Return the smallest integer not less than X
|
ceil
|
ceil(3.7)
|
Return the integer nearest to X
|
round
|
round(1.9)
|
Truncate fractional portion of X and return the integer portion
|
fix
|
fix(pi)
|
Stats Functions
Task
|
Example
|
Function
|
Uniform random numbers btw 0 and 1 (both excluded)
|
rand
|
rand(3,5)
|
Normal(0,1) random numbers
|
randn
|
randn(1,3)
|
Gamma distribution
|
randg
|
randg
|
Exponential distribution
|
rande
|
rande(1,10)
|
Poisson distribution
|
randp
|
randp(0.5,3,3)
|
Min value by column
|
min
|
min(A)
|
Max value by column
|
max
|
max(A)
|
Constants
Name
|
Expression
|
Default Variable
|
ans
|
Pi
|
pi
|
Euler's number
|
e
|
Imaginary number
|
i, j and I
|
Infinity
|
inf
|
Not a Number
|
NaN
|
machine precision
|
eps
|
true/false
|
logical 1/0
|
Logical Operators
Expression
|
Operator
|
is greater than
|
>
|
is less than
|
<
|
is greater than or equal to
|
>=
|
is less than or equal to
|
<=
|
is equal to
|
==
|
is not equal to
|
∼= or !=
|
AND with short circuiting
|
&&
|
with short circuiting
|
||
|
AND
|
&
|
OR
|
|
|
NOT
|
∼
|
Auxiliary Functions
Task
|
Function
|
Check a scalar
|
isscalar(a)
|
Check a vector
|
isvector(b)
|
Check a matrix
|
ismatrix(b)
|
is func available
|
is TAB TAB
|
Type info
|
typeinfo(b)
|
String Functions
Task
|
Function
|
Example
|
Compare 2 strings
|
strcmp
|
strcmp("hello","Hello")
|
Import & Export Data
Task
|
Command
|
Example
|
Read the matrix DATA from a text file
|
dlmread (FILE, SEP, R0, C0)
|
dmlread("virus.dat",",",1,1);
|
Write data to a text file
|
dlmwrite (FILE, M, DELIM, R, C)
|
dlmwrite("out.txt",yhat,";",1,1);
|
Read the csv files
|
csvread (FILENAME, DLM_OPTS)
|
csvread("input.csv");
|
Write csv files
|
csvwrite (FILENAME, X, DLM_OPTS)
|
csvwrite("output.csv", yhat);
|
Defining Functions
Simplest Form
function name
body
end
Example:
function wakeup
printf ("\a");
end
Passing Params
function name (arg-list)
body
end
Example:
function wakeup (message)
printf ("\a%s\n",
message);
end
wakeup ("Rise and shine!");
Return Single Value
function ret-var = name (arg-list)
body
end
Example:
function retval = avg (v)
retval = sum (v) / length (v);
end
Return Multiple Values
function [ret-var1,ret-var2,…,ret-varn] = name (arg-list)
body
end
Example:
function [mu,sigma] = basicStat(X)
mu = mean(X);
sigma = std(X);
end
Statements
IF Statement
if (condition)
then-body
elseif (condition)
elseif-body
else
else-body
end
Example:
if (rem (x, 2) == 0)
printf ("x is even\n");
elseif (rem (x, 3) == 0)
printf ("x is odd and divisible by 3\n");
else
printf ("x is odd\n");
end
Note that the elseif
keyword must not be spelled else if, as is allowed in Fortran. If
it is, the space between the else and if will tell
Octave to treat this as a new if statement within another if
statement's else clause
SWITCH Statement
switch (X)
case 1
do_something ();
case 2
do_something_else ();
otherwise
do_something_completely_different ();
end
Example:
A = 7;
switch A
case { 6, 7 }
printf ("variable is either 6 or 7\n");
otherwise
printf ("variable is neither 6 nor 7\n");
end
One advantage of using the switch statement compared to using
if statements is that the labels can be strings
switch (X)
case "a string"
do_something
...
endswitch
WHILE Statement
while (condition)
body
end
Example:
fib = ones (1, 10);
i = 3;
while (i <= 10)
fib (i) = fib (i-1) + fib (i-2);
i++;
end
DO-UNTIL Statement
do
body
until (condition)
Example:
fib = ones (1, 10);
i = 2;
do
i++;
fib (i) = fib (i-1) + fib (i-2);
until (i == 10)
FOR Statement
for var = expression
body
end
Example:
fib = ones (1, 10);
for i = 3:10
fib (i) = fib (i-1) + fib (i-2);
end
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