At the risk of alienating some of our readers, I am enclosing a link to a Yahoo Youtube video
about kidnapper brigands in Mindanao beheading their captives.
It is not for the faint of heart. Here is the link: Youtube
Monday, November 14, 2011
Thursday, November 10, 2011
Why I did not watch Wowowie tv show
It seems that the overall level of intelligence will be lowered when you watch this tv show. If I did catch it public places or buses, I only do intently focus on it when the sexily clad dancers do their thing. Anyways, here is a series of questions and the funny or smart answers the emcee participants have dissed out. (Translated from Tagalog.)
- If those who eat greens are called vegetarians, what do you call those who eat humans? Ans. humanitarian!
- What are Michael and Raphael?
Ans. Ninjas
- In what country most Hindus come from?
Ans. Hindunesia!
- What do you take out from an egg before you cook them?
Ans. Hair! (expecting the "shell")
- If H20 is water, what is CO2?
Ans. Cold water!
Complete the sentence: Beauty is in the eye of the ____? Ans. Tiger! (Beholder is the right answer!)
Labels:
Humor
Wednesday, November 9, 2011
R quick reference
- Help and demos.
The home page of R is http://www.r-project.org
type help.start() to use a browser to view standard documentation
type demo() to view demos of the capabilities of R.
type ?topic to view manual pages of an R function or library.
- To recover last computed expression in R:
Use the special variable .Last.value
- How do I display floating point number to a specified number of digits?
options(digits = 10)
when you want finer control, you may use sprintf("%.nf", value) where n must be replaced by
the numerical value of the number of digits.
- Creating sequences.
X <- seq(1,100) X <- seq(1, 100, by = 3) X <- seq(1, 100, length=5) Note that the spacing in sequence X is given w = (endvalue, startvalue)/(length - 1). - What are the elementary operations on sequences or vectors.
All variables in R are vectors! Two vector operands are first set to the same length,
recycling elements if necessary.
Arithmetic operations +, -, *, / works pairwise.
Functions or operations applied to a vector result in new vector.
X^2 gives a new vector with the square of the elements in original X.
X*X gives the same results!
- To determine the number of elements in a vector
length(X)
- To extract the kth element(indexing starts at 1)
X[k]
- To return a vector with the kth element deleted.
X[-k]
- To return a vector with some elements deleted.
X[-c(1,3, 5)] will delete the elements at the first, third and fifth position.
To repeat a vector.
rep(X, ntimes) will return a new vector repeated ntimes.
X <-c(1,2) rep(X, 5) will display [1] 1 2 1 2 1 2 1 2 1 2 - To concatenate two or more vectors
c(X,Y, Z)
- To compute the product of all elements in a vector.
prod(X)
- To assign an element v at a specific position k.
X[k] <- v Not that if k is greater than length of X, X will be enlarged! To filter elements of X meeting a condition. X[condition] For example, X[X > 5] will display a new vector with element values > 5.
To sum all elements in a vector
sum(X)
To sort a vector
sort(X)
- How do you mark lines as comments in R?
Start each line (leading spaces are ignored) with a #.
- How do I edit a user defined function definition?
Method 1. use fix(function_name)
You mispelled length(X):
gm <- function(X){ exp(sum(log(X))/lenggth(X)) } use fix(gm). edit the offending line and save file. Now type gm. The erroneous definition now has been saved! Method 2. use edit(function_name) Type gm <- edit(gm) This has the same behavior as fix. Method 3. body(function_name)) for one line definitions, this may work out well from the command line. body(gm) <- expression({exp(sum(log(X))/length(X))}) Method 4. as.list(body(function_name))) for multiline definitions, use as.list, taking into note that the line 1 is always the starting {. Hence the first line of the function is body(function_name[[2]]. To change a specific line, body(function_name[[line#+1]] <- substitute(newexpression). Reference:http://stackoverflow.com/questions/2458013/what-ways-are-there-to-edit-a-function-in-r - What are reserved variables in R?
Do not use c, t, q, F, T
- In conditional tests, what are the available comparison operators?
!expr NOT
>,<, != inequalities = equality - Does R provide bitwise operators?
bitAnd(a, b)
bitOr (a, b)
bitXor(a, b)
All functions above works on 32 bitwide unsigned integers
- What are the available programming control structures in R?
conditional if
if (condition) expr
conditional if-else
if (cond) expr1 else expr2
switch
switch(expr, ...)
ifelse
ifelse(test,yes,no)
looping constructs and cotrol statements:
for (var in seq) expr
while (cond) expr
repeat expr
break
next
- How do I input a program or data file to R?
source(filename)
- How do I redirect output to a file from R?
sink(outfilename)
- What are the functions for handling libraries or packages?
library() # list all available packages
library(lib.loc = .Library) # list all packages in the default library
library(help = splines) # documentation on package 'splines'
library(splines) # load package 'splines'
require(splines) # the same
search() # "splines", too
detach("package:splines")
- How do I install contributed packages?
install.packages() interactive install
install.packages(pkgname) install a specified package.
remove.packages(pkgname) removes a package
library() # list all available packages
library(lib.loc = .Library) # list all packages in the default library
library(help = splines) # documentation on package 'splines'
library(splines) # load package 'splines'
require(splines) # the same
search() # "splines", too
detach("package:splines")
Standard repositories are "http://cran.r-project.org"and its mirror site
http://lib.stat.cmu.edu/R/CRAN.
You should be root to install the libraries systemwide.
Labels:
R quickref
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