An Introduction to R 1.1 Getting started

Transcription

1 An Introduction to R 1.1 Getting started Dan Navarro (daniel.navarro@adelaide.edu.au) School of Psychology, University of Adelaide ua.edu.au/ccs/people/dan DSTO R Workshop, 29-Apr-2015

2 There s a book

3 What is this all about?

4 What is R? R is a statistical programming language A comparison: SPSS relies on menus, R is command based SPSS is expensive, R is free SPSS is centrally designed, R has a small core and thousands of contributed packages SPSS usually has one way to do an analysis, R typically has many SPSS is designed to be user friendly, R expects a certain level of statistical and programming skill

5 Should I learn R? Pro: Attractive $0 price tag Freedom to do your analysis, your way (it s a programming language, not a fixed suite of tools) Tools for reproducible research (Rstudio lets you publish your analyses via R markdown) All the cool kids are doing it (new statistical tools get published as R packages first) Everyone else is too (massive rise)

6 Should I learn R? Pro: Attractive $0 price tag Freedom to do your analysis, your way (it s a programming language, not a fixed suite of tools) Tools for reproducible research (Rstudio lets you publish your analyses via R markdown) All the cool kids are doing it (new statistical tools get published as R packages first) Everyone else is too (massive rise) Con: It s harder to learn than SPSS

7 The rise of R

8 The rise of R

9 The rise of R

10 The rise of R Software used in data analysis competitions

11 Getting R R website: Windows installer file: Mac installer file:

12 What is Rstudio? Unlike SPSS, R is not an application. It is a programming language R can be accessed via several applications: The default application (if you must) The terminal window (if you re old school) Rcommander (if you want to force R to be SPSS) Rstudio (if you want something slick and powerful)

13 Screenshots: R.app (Mac)

14 Screenshot: R.exe (Windows)

15 Screenshot: Terminal

16 Rstudio is a (free) front end to R. It s intended to provide the same user experience regardless of what kind of computer you re using Download from the Rstudio web site:

17 Why Rstudio? Pro: Same interface on Windows, Mac & Linux Lots of little tools to simplify some of the more tedious tasks in data analysis Excellent web authoring tools (via R markdown)

18 Why Rstudio? Pro: Same interface on Windows, Mac & Linux Lots of little tools to simplify some of the more tedious tasks in data analysis Excellent web authoring tools (via R markdown) Con: It doesn t have a menu system for analysis functionality: menus are for pragmatic work only (I think that s actually a pro- myself)

19 Rstudio is divided into several panels

20 Minimising and maximising panels:

21 Switching between panels:

22 Menu system

23 Writing scripts for each analysis

24 The console is the main thing. That s R running in this panel.

25 Loading data Descriptive statistics ANOVA

26 Basic commands

27 R is (usually) an interactive system You type your commands here when you hit enter, R immediately executes the command and displays the results on screen.

28 Our first command... The > is the command prompt > [1] 13

29 Our first command... This is a command > [1] 13

30 Our first command... > [1] 13 The number 13 is the output (don t worry about the [1] for now)

31 Try it yourself (Exercise 1.1.1)

32 Simple calculations + addition - subtraction * multiplication / division ^ taking powers These are referred to as operators (each operator is used to carry out a particular kind of operation)

33 Simple calculations + addition - subtraction * multiplication / division ^ taking powers These are referred to as operators (each operator is used to carry out a particular kind of operation) > (6-4) / 2 [1] 1 > 6 - (4/2) [1] 4 When performing multiple calculations you can use parentheses to make sure R performs the calculations in the desired order (Note: Without parentheses, the order is: ^ first, then * and / second (left to right), and then + and - last (left to right). No-one remembers this at first.)

34 Try it yourself (Exercise 1.1.2)

35 == equality!= inequality > greater than >= greater than or equal to < less than <= less than or equal to Logical statements

36 Logical statements == equality!= inequality > greater than >= greater than or equal to < less than <= less than or equal to > 10 < 100 [1] TRUE > == 5 [1] FALSE

37 Logical statements == equality!= inequality > greater than >= greater than or equal to < less than <= less than or equal to & AND OR! NOT > 10 < 100 [1] TRUE > == 5 [1] FALSE

38 Logical statements == equality!= inequality > greater than >= greater than or equal to < less than <= less than or equal to > 10 < 100 [1] TRUE & AND OR! NOT > (10 < 100) (2 + 2 == 5) [1] TRUE > (10 < 100) & (2 + 2 == 5) [1] FALSE > == 5 [1] FALSE

39 Try it yourself (Exercise 1.1.3)

40 Functions There are not enough symbols on the keyboard to do everything you might want to do... so there are only a few operators Most things are functions

41 Functions There are not enough symbols on the keyboard to do everything you might want to do... so there are only a few operators Most things are functions Example: logarithms > log( 32 ) [1] The function is called log. - The 32 is the argument to the function.

42 Some functions that you might see on a scientific calculator sqrt() - Square root round() - Round a number log() - Logarithm exp() - Exponentiation abs() - Absolute value

43 Functions with multiple arguments - Many functions can take more than one argument; - Separate the arguments with commas.

44 Functions with multiple arguments - Many functions can take more than one argument; - Separate the arguments with commas. Argument #1: The number that needs to be rounded Argument #2: How many digits to round it to? > round( , 2 ) [1] 3.14

45 Arguments have names - Most of the time, the arguments have names, - You can use the names when typing commands

46 Arguments have names - Most of the time, the arguments have names, - You can use the names when typing commands The number that needs to be rounded is called x The number of digits to round to is called digits > round( x = , digits = 2 ) [1] 3.14 (When you specify the names of the arguments, R doesn t care what order you type them in...but if you drop the names, then you must make sure you type them in the correct order)

47 Some arguments have defaults - A lot of arguments have default values. - If you don t tell R what value to use, it uses the default

48 Some arguments have defaults - A lot of arguments have default values. - If you don t tell R what value to use, it uses the default > round( x = ) [1] 3 The default number of digits to round to is digits = 0, so that s what R uses here

49 Try it yourself (Exercise 1.1.4)

50 Getting help!

51 Help documentation

52 Google it!

53 End of this section