1.4 Writing and executing R code

R code is the backbone of data analysis in this programming language. Learning to write and execute it effectively is crucial for your success. This section covers the basics of R syntax, including variables, functions, and operations.

You'll also discover how to run your code in different environments, manage your workspace, and handle errors. These skills form the foundation for more advanced R programming techniques you'll encounter later in the course.

Basic R Syntax

Core Syntax Elements

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• R syntax follows a clear and consistent structure enabling efficient data manipulation and analysis
• Comments begin with

  #

  symbol, allowing developers to annotate code for clarity and documentation
• Variables store data values, assigned using

  <-

  or

  =

  operators (

  x <- 5

  or

  x = 5

  )
• Functions perform specific tasks, called using parentheses and arguments (

  function_name(argument1, argument2)

  )

Variable Types and Operations

• Numeric variables store numbers (

  x <- 10.5

  )
• Character variables contain text strings, enclosed in quotes (

  name <- "John"

  )
• Logical variables hold TRUE or FALSE values (

  is_student <- TRUE

  )
• Vector creation uses

  c()

  function to combine multiple values (

  numbers <- c(1, 2, 3, 4, 5)

  )
• Arithmetic operations include addition (

  +

  ), subtraction (

  -

  ), multiplication (

  *

  ), and division (

  /

  )
• Comparison operators evaluate conditions (

  ==

  ,

  !=

  ,

  <

  ,

  >

  ,

  <=

  ,

  >=

  )

Function Basics and Examples

• Built-in functions provide pre-programmed operations (mean, sum, length)
• User-defined functions allow custom operations creation
• Function structure includes name, arguments, and body (

  my_function <- function(x, y) { x + y }

  )
• Function arguments can have default values (

  greet <- function(name = "User") { paste("Hello", name) }

  )
• Return values specify function output (

  return()

  statement or last expression)

Executing R Code

Running Code in R Environment

• Interactive execution occurs in R console, entering commands one at a time
• Script files (.R extension) allow multiple lines of code to be run together
• Source command executes entire script file (

  source("script_name.R")

  )
• RStudio provides integrated development environment for R, offering code editor and console in one interface
• Code chunks in R Markdown documents combine code and documentation

Command History and Workspace Management

• Command history stores previously executed commands, accessible using up arrow key

• history()

  function displays recent commands in console
• Save workspace image preserves current R session variables and data (

  save.image()

  )
• Load previously saved workspace restores saved session (

  load()

  )
• Clear workspace removes all objects from current session (

  rm(list = ls())

  )

Error Handling and Debugging

• Error messages provide information about code issues, helping identify and fix problems
• Warning messages alert potential issues without stopping code execution
• Debugging tools assist in identifying errors (browser() function, RStudio debugger)
• Common errors include syntax errors, object not found, and incorrect data types
• Error tracing helps locate source of errors in complex code structures

Working Directory and File Management

• Working directory sets default location for file operations

• getwd()

  function displays current working directory

• setwd()

  function changes working directory (

  setwd("/path/to/directory")

  )
• Relative file paths reference files relative to working directory (

  read.csv("data/myfile.csv")

  )
• Absolute file paths specify complete file location (

  read.csv("/home/user/documents/data/myfile.csv")

  )