Introduction to Exploratory Descriptive Data Analysis in SPlus

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Introduction to Exploratory Descriptive Data
Analysis in S-Plus

• Jagdish S. Gangolly
• State University of New York at Albany

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Simple Structures I Arithmetic Operators

• Arithmetic Operators
• , /, , and -.
• Avoid amguity by using parantheses, eg., (72)3,
  since 72313 and not 27.
• Multiplication and division are evaluated before
  addition subtraction. Raising to a power ( or
  ) takes precedence over everything else.

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Simple Structures I Assignments

• Assignments
• X lt- 3 or 3 -gt x or x_3 or x3
• Not a good idea to use underscore for assignment
  or the equals sign.
• To see the value of a variable x
• X or print(x)
• To remove a variable x
• Rm(x)

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Simple Structures II Concatenation

• Concatenation
• Used to create vectors of any length
• gt X lt- c(1.5, 2, 2.5)
• gt X
• 1.5 2.0 2.5
• gt X2
• 2.25 4.00 6.25
• .c can be used with any type of data

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Simple Structures III Sequence

• Sequence command
• Seq(lower, upper, increment)
• Some examples
• seq(1,35,5) 1 6 11 16 21 26 31
• seq(5,15,1.5) 5 6.5 8.0 9.5 11 12.5 14.0
• seq(50,25,-5) 50 45 40 35 30 25

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Simple Structures IV Replicate

• Replicate command to generate data that follow a
  regular pattern
• Some examples
• rep(8,5) 8 8 8 8 8
• rep(8, 5) 8 8 8 8 8
• rep(c(0,ab),2)0 ab 0 ab
• rep(14, 14) 1 2 2 3 3 3 4 4 4 4
• Rep(13, rep(2,3)) 1 1 2 2 3 3
• Rep(c(1,8,7),length5))1 8 7 1 8

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Simple Structures V Expressions

• gt X lt- seq(2,10,2)
• gt Y lt- 15
• gt Z lt- ((3x22y)/((xy)(x-y)))(0.5)
• gt X
• 2 4 6 8 10
• gt Y
• 1 2 3 4 5
• gt Z
• 2.160247 2.081666 2.054805 2.041241 2.033060

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Simple Structures VI Logical Operators

• lt Less Than
• gt Greater than
• lt Less than or equal to
• gt Greater than or equal to
• Equal to
• ! Not equal to

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Simple Structures VII Index Brackets

• Square brackets are used to index vectors and
• matrices.
• gt x lt- seq(0,20,10)
• gt x2
• 10
• gt x5
• NA
• gt xc(1,3)
• 0 20
• gt x-1
• 10 20

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Data Manipulation I Frames matrices I

• Matrices two-dimensional vectors (have row and
  column indices
• Arrays General data structure in S-Plus
• Zero-dimensional scalar
• One-dimensional vector
• Two-dimensional matrix
• Three to eight-dimensional arrays
• The data in a matrix must all be of the same
  datatype (usually numeric datatypes)

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Data Manipulation I Frames matrices II

• The columns in dataframes can be of different
  datatypes
• Lists The most general datatype in S-Plus

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Data Manipulation I Matrices I

• Reading data
• S-Plus is very finicky about format of input data
• To read a table
• Read.table(filename) The first column must be
  rownames
• The first row must be column names
• The top left cell must be empty
• Space/tab the default column delimiters
• See the example fasb103.txt in the directory
  /db4/teach/acc522/ on the machine
  cayley.ba.albany.edu and play around with it.

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Data Manipulation I matrices II

• Read.table and as.matrix()
• x lt- Read.table(filename)
• as.matrix(x)
• Enter data directly
• Matrix(data, nrow, ncol, byrowF)
• Example
• x lt- Matrix(16, nrow2, byrowT)
• dim(x) (2 X 3)
• Dimnames(x) (NULL)

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Data Manipulation I matrices III

• Elements of matrices are accessed by specifying
  the row and column indices.
• Example
• data lt- c(227,8,1.3,1534,58,1.2,2365,82,1.8)
• dountries lt- c(austria, france, germany)
• variables lt- c(gdp, pop, inflation)
• country.data lt- matrix(data,nrow3,byrowT)
• dimnames(country.data)lt- list(countries,variables)
  
• Country.data12,23 pop and inflation of
  austria france

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S-Plus Graphics I

• To open a graphics window
• motif()
• You can adjust the color scheme and print options
  through the drop-down menu on the motif window.
• To plot two variables x and y,
• plot(x,y)
• Example (sine curve)
• plot(1100, sin(1100/10))