Using R

1
Using R

• Harry R. Erwin, PhD
• School of Computing and Technology
• University of Sunderland

2
Resources

• Crawley, MJ (2005) Statistics An Introduction
  Using R. Wiley.
• Gonick, L., and Woollcott Smith (1993) A Cartoon
  Guide to Statistics. HarperResource (for fun).

3
Lecture Outline

• R as a statistical calculator
• Creating data
• Graphing and plotting
• Statistical distributions
• Dataframes
• Summarising data

4
Using R

• We will work through a few examples of
  statistical calculations and creating data.
• ylt-c(3,7,9,11)
• zlt-scan()
• alt-16
• blt-seq(0.5,0.0,-0.1)
• rep(value,count) creates a vector with value
  count times.
• gl(upTo,repeats) can be used to generate factor
  data

5
Graphics

• Examples of plot()
• ?par for help on graphics parameters

6
Working with Dataframes

• R works with data in dataframes, objects with
  rows and columns.
• Each row is an observation or a measurement
• Each column contain the values of a variable.
• Variable types include numbers, text (factors),
  dates, or logical variables.
• Columns have names. Rows have row.names.

7
Reading a Dataframe

• wormslt-read.table("worms.txt", header T,
  row.names 1)
• attach(worms)
• names(worms)
• If the row.names or the names are bad, you can
  set them to values.
• worms
• summary(worms)

8
Selecting Rows or Columns

• worms,13 for all the rows and columns 1-3.
• worms515, for the middle rows
• wormsAreagt3 Slope lt 3, for logical tests
• To sort a dataframe, you have to designate the
  columns to be sorted and the column to base the
  sort on wormsorder(worms,1),16
• Example of a reverse sort

9
Vectors

• ylt-c(5,7,7,8,2,5,6,6,7,5,8,3,4)
• zlt-131
• Try mean, var, range, max, min, summary, IQR,
  fivenum
• y3
• y37
• yc(3,5,6,9)
• y-1
• y-length(y)
• yygt6
• zygt6
• yy3!0

10
Vector Operations

• is vector multiplication
• If they are not the same length, the shorter
  vector is repeated as needed.
• To join vectors, use the c() function
• ?c
• Subscripting can be based on a number, vector, or
  test.
• To drop an element, subscript with a minus sign
  in front
• Vectors can be combined with cbind() and rbind()

11
Arrays, etc.

• Like vectors or dataframes with multiple
  dimensions
• Lists can be used to combine data of different
  types.
• val lt- list(varnamevalue,)
• Although vectors are subscripted using , lists
  are subscripted with
• Factors are special
• citizen lt- factor(c("US","US","UK))
• Examples from book.

12
Sorting and Ordering

• Never sort a dataframe column on its own. The
  other columns are not sorted.
• So dont use sort()
• Instead use order(), since it leaves the
  dataframe unmodified. It returns a vector of
  subscripts, not values, but then you can apply
  the dataframe to the reordered vector to show it
  in the new order.

13
Table

• Suppose vals is a collection of vectors
• table(vals) reports the count of each unique
  value
• tapply takes three arguments
• Variable or dataframe to be summarised
• Variable by which the summary is classified
• Function to apply
• Examples

14
Data Manipulation

• To convert a continuous variable into a
  categorical variable, use cut(vals,levels)
• You can also specify the break points
• split() can be used to generate a list of vectors
  on the basis of the levels of a factor.
• Example

15
Saving your Work

• history(Inf)
• savehistory("filename")
• save(listls(), file "filename")
• Tidying up
• rm(var) any temporary variables
• detach(dataframes)
• rm(listls()) will clean up everything

16
Conclusions

• There are other tools and languages
• Minitab
• SAS
• Spreadsheets
• Use what youre comfortable with.
• But professional statisticians use R.