R - Turorial II

Lists

• Collection of Objects of same or mixed type.List may also contain vector or other lists.
• Create a list using the funtion list().
• The following example shows operations that can be performed on a list.

> alphabets=list(a="apple",b="ball",c="cat")
> alphabets
$a
[1] "apple"
$b
[1] "ball"
$c
[1] "cat"

> alphabets[[1]]
[1] "apple"
 

> alphabets$a
[1] "apple"
 

> length(alphabets)
[1] 3
 

> alphabets[["a"]]
[1] "apple"

• Double brackets [[.]] are used for getting a single element. names are not returned.  single brackets [.]  can be used for subscripting. 
• When lists are formed from objects, the elements use to form the list are copied.
• function c() can be used to combine lists to form an object of type list.

Data Frame

• Lists having class 'data.frame' are called data frames.
• the components of the list must be vectors, factors, numeric matrices, lists or other data frames. vector structures appearing as variables in the dataframe must all have same length. Matrix structures appearing as variables in the dataframe must all have same row size.
• data frames can be created using function data.frame

R - Tutorial I

Basics

• Start R in Windows using the program menu.
• To quit :  q().
• to call help for a function. help([function]) or ?[function]. use double quotes to escape special characters and tokens. e.g. ?"for".
• objects() or ls() to obtain list of objects stored. rm([object]) to remove object.
• x= 1:4 create sequence of numbers. 1 2 3 4. colon has highest priority in expressions.
• seq() function can also be used to generate sequences. it has five arguments to, from, by (increment), length.out (length of seq), along.with (take length from length of this argument).
• R objects have mode i.e type for "atomic" objects ( numeric, complex, logical, character and row ). Mode for list objects is list. Other modes are functions and expressions. Objects also have a property called length. 
• as.integer(x) coerces x to integer. There are numerous othe functions of type as.* for different coercions. Type apropos("as.*") in R windows to know more.
• Each object has a class. for vectors it is the same as mode. class can be used for object oriented type of programming. method dispatch is based on the class of the first variable passed to the method. an example of a class is the value returned from fitting linear model using 'lm'. The output of the method is an object of class 'lm'.
• Factors can by used to prepare categorical values for statistical analysis. the function factor(a) assigns integers to unique values (levels) in the vector a and stores the variable factor(a) as a vector of integers and also stores mapping between the integer values to the actual values in a. factor(a) can then be used in statistical analysis (summary function etc). the factors are stored in natural order of the elements in a. To explicitely provide another order use the ordered function. Read more at: link1 , link2

Vectors

• Create a vector named a. a = c(1,2,3,4). c is the generic function to combine arguments. output type is the highest of NULL < raw < logical < integer < real < complex < character < list < expression

b=c("!",2,a) = "!" "2" "1" "2" "3" and b=c(2,a) = 2 1 2 3.

• Vector arguments can have names. names(a) = c("first","second","third") 

> a
 first second  third
     1      2      3

• +,-,*,/ : Individual elements are added. shorter vector are recycled

> a=c(1,2,3)
> b=c(4,5)
> a+b
[1] 5 7 7
Warning message:
In a + b : longer object length is not a multiple of shorter object length

• Functions - max (maximum value), min (minimum value), range =c(min(x).max(x)), length (length of vector), sum (total of all elements), prod (product of all elements), mean = sum/length, var(simple variance), sort (sorting in ascending order), pmax (vector or higest elements in individual vectors of the argument)
• Logical vectors contain TRUE, FALSE and NA.
• missing values are given as NA. is.na(a) returns a vector of same length as a and values FALSE if a contains 'NA' or 'NaN' , and TRUE otherwise.
• function paste() can be used to combine strings of two or more vectors one by one. vectors are recycled if required

>  paste(c("X","Y"), 1:10,2:5)
 [1] "X 1 2"  "Y 2 3"  "X 3 4"  "Y 4 5"  "X 5 2"  "Y 6 3"  "X 7 4"  "Y 8 5"  "X 9 2"  "Y 10 3"

• Index Vector: in the example below, b is the index vector in various forms.

> a=c(1,2,3,4,5,6,7,8,9,10)
> b=c(TRUE,FALSE,FALSE,TRUE,TRUE,TRUE,FALSE,TRUE,FALSE)
> a[b]
[1]  1  4  5  6  8 10
> b=c(1:5)
> a[b]
[1] 1 2 3 4 5
> b=-(1:5)
> a[b]
[1]  6  7  8  9 10

R and Java - JRI Using Netbeans

Setting up R-Java in Netbeans is pretty straight forward. For those who need a walkthough here are the steps.

1. Download and install R (for this example version 2.12.2). install rJava package. 
2.  Download and install Netbeans. 
3. In Netbeans Create a new java project. we will call it RJava.
4.  From the [R_HOME]>/library/rJava/jri/examples folder, copy the file rtest.java into the project.
5. Create a library in NetBeans and add the following jars to the library. - JRI.jar, JRIEngine.jar, REngine.jar. These files are present in [R_HOME]/library/rJava/jri/. Here's how the project looks like
   
6. Minimize Netbeans. Add R_HOME variable (right click my computer-> properties-> Advanced ->Environment variables) R_HOME should point to the location where R is installed.
7. edit the PATH variable and append the following (i) [R_HOME]\library\rJava\jri and (ii) [R_HOME]\bin
   

That's it. Right click on rtest.java and click on 'Run File'.

R and Java - JRI using eclipse on 64 bit machines

Update - Check out the new RJava Eclipse Plugin.
The steps to install rjava on a 64 bit machine is not very different from installing it on a 32 bit machine. however, here are the exact steps.

1. Install 64 bit java.
2. Install R 2.12.X
3. Start R and install the rjava package using the package installer.
4. Start eclipse. Create a project called RTest. copy the Rtest.java and RTest2.java files from the examples folder of rjava (R-2.12.2\library\rJava\jri\examples)
5. Create a lib folder in the RTest project and copy the jri.jar file from R-2.12.2\library\rJava\jri into it.
6. add jri.jar to the classpath of the project. ensure that the project compiles without error.
Here's the folder structure


7. Before running the RTest.java class, the run configuration needs to be edited. open the run configuration by clicking on run->run configuration. select Rtest as project and rtest as the main class. click on environment and add the variable 'PATH' . the path should contain paths to the following
a. the bin directory of R (64) : \R-2.12.2\bin\x64;

b. The jri directory for rjava (64bit) : \R-2.12.2\library\rJava\jri\x64.


8. click on apply and then run.

Oracle BI applications - Installation

In this post we look at installing and configuring Oracle BI Applications. I managed to install the application on an intel core 2 duo laptop with 2 GB RAM, Windows Vista machine.
We would need source data to view the dashboard for BI apps, the source data can be obtained from Oracle E business suite vision database. This post will explain how to install the Oracle E business suite for the purpose of getting the vision database up and running.

Step 1: Installing the Oracle E Business Suite (EBS).

• EBS can be downloaded from the oracle site. It is a huge download with multiple files (42G). Here's an article that describes what files to download.
• Once the files are downloaded we need to extract them to a staging directory. the extract can be done manually using an unzip utility.

• Extract the files to the folder structure as shown above.
• Start the rapidwiz wizard for ebs installation

If the system uses another instance of oracle it would be a good idea
to shift the ports by 3. in this example, since we would be using
other oracle instances for informatica and dac, i have shifted the ports
by 3



For this example i have installed the ebs instance on an external USB
hard drive since the install requires a lot of space.




Select Vision Demo Database for database type, this will install the sample
data that we required to load into OBIA



EBS installation requires cygwin and VB. provide the appropriate paths.





The OS User group check fails for Vista for some reason.
lets ignore them for now.






THe installation process may take a long time. My installation failed after
step 3 above. however, the vision database is installed before that.
since we need only the database, we can ignore the rest of the install.


Step 2: The next step is to prepare the oracle instances that will be used by informatica and DAC. It would be a good idea to use different users for different areas

Database type	Name
Informatica repository	dwa
DAC repository	dacrep
OBIA DATAwarehouse	obdw
source	vis

THe Name refers to the oracle user. vis refers to the vision database instance. note that
the database can be accessed by apps/apps

• Create and SSE_ROLE as described in section 4.4.1.1 of Installation Guide for Informatica PowerCenter Users Version 7.9.6.1 (install guide)
• set the NLS_LANG variable as described in section 4.4.2.1 of install guide.

STEP 3 : Installing Oracle BI APPS