Transcript Statistical Software

Statistical Software
An introduction to Statistics Using R
Instructed by Jinzhu Jia
Chap 2. Programming with R
 Workspace
 Working directory
 Input and output
 Flow control
 Functions
 Packages
 Writing R scripts
Workspace
 All of the objects are the content of the R workspace
 What objects do you have in your R workspace ?
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objects()
ls()
ls.str()
library(lsr) ## Note: the first time we see using a package
 who()
## Anytime you want to use who(), please use the
command ``library(lsr)” first. Will learn more later
 Differences?
Removing variables
 rm(X,Y) ## variabes X and Y will be removed from the
workspace
 rm(list = c(‘X’,’Y’)) ## the same as the above command
 rm(list = ls())
Working directory
 Working directory specifies what folder your data will
be read from or save to.
 getwd() ## wd denotes working directory
 setwd(‘./newfolder’) ## ./ denotes the current folder
 You can also use Misc->Changing working directory to
choose your folder in your MAC
 list.files() ## list all the files in the current wd.
Reading data
 read.csv()
## most frequently used
 read.table() ## frequently used
 scan() ##
 readLines() ##
 data() ## R has a few data sets in its packages
## this function lists dataset names stored in the
Try:
workspace, such as
 data(‘data set name’) ## loads the data
data()
data(Airpasse
nengers)
ls()
Saving data
 write.csv()
 write.table()
 save() ## save a few variables
 save.image() ## save the whole workspace
 load()
 See help for the details
R script
 It is a text file
 You can use it to write all your R commands
 Write your own package
 File->New Scrip ## you will get an empty script file
 source(rscipt_File)
Flow Control
 while loop
 while ( CONDITION )
{ STATEMENT1
STATEMENT2
ETC
}
 Note: { } is a block of statements; if you do not use {},
only the first statement will be executed in the loop
for loop
 for ( VAR in VECTOR )
{ STATEMENT1
STATEMENT2
ETC }
 break() ## the same as in C
 next() ## C uses continue()
Conditional statements
 if ( CONDITION )
{
STATEMENT1
STATEMENT2
ETC
}
 switch()
if ( CONDITION )
{
STATEMENT1
STATEMENT2
ETC }
else {
STATEMENT3
STATEMENT4
ETC
}
Rule of switch()
 switch(ExpR,….)
 Expr: an expression evaluating to a number or a
character string
 If the value of EXPR is not a character string it is
coerced to integer. The corresponding element of ….
will be evaluated
 If EXPR evaluates to a character string then that string
is matched (exactly)to the names of the elements in ....
Functions
 FNAME <- function ( ARG1, ARG2, ETC )
{
STATEMENT1
STATEMENT2
ETC
return( VALUE )
}
Binary operator
 %*% ## matrix multiplication
 %% ## modulus 5%%2 = 1
 %/% ## integer division 5%/%2 = 1
 %in% ## ‘a’ %in% c(‘a’,’b’,’c’) = T
 Create your own binary operator
 ‘%+%’ <- function(s1,s2){}
Default parameters
 ? Seq
 seq(from = 1, to = 1, by = ((to - from)/(length.out - 1)),
length.out = NULL, along.with = NULL, ...)
 We see a few parameters in function seq(), each of wich
has default parameters.
 Example: mysub = function(x,y=1){z = x-y}
mysub(2) = mysub(2,1) = mysub(x=2)
Recursive function
 Example:
 factorial <- function(x){ if(x==1) return( 1) else
return(x*factorial(x-1)) }
Packages
 A package is a collection of objects
 It usually completes one special task
 Use a package: libray(‘package name’)
 Install a package: install.packages(‘package name’)
Homework
 Find all of the pairs of twin primes less than 10^6 using R and
report the total number.
 Print a calendar for any given month and year as input.
For example: mycal(2014,3) will give you a table like this:
Hint: ? as.Date()
Help: http://www.statmethods.net/input/dates.html
 Send your code and results to [email protected]