Concepts for R

R is a programming language and environment primarily used for statistical computing and graphics. Developed by Ross Ihaka and Robert Gentleman in the early 1990s, R provides a wide range of statistical and graphical techniques, including linear and nonlinear modeling, time-series analysis, and clustering. R's syntax is optimized for data analysis tasks, with built-in support for data manipulation, visualization, and statistical modeling. Key features include an extensive collection of packages contributed by the R community through the Comprehensive R Archive Network (CRAN), allowing users to access a vast array of specialized tools and algorithms for various statistical and data analysis tasks. R's popularity in academia, research, and data-driven industries such as finance and healthcare is attributed to its flexibility, robustness, and the rich ecosystem of packages available for data analysis and visualization.

• Print Text

  print('Hello World!')
  print("Hello World!")

• Comments

  # one line comment
  
  # multi 
  # line 
  # comment
  

• Variables

  carCount <- 2
  name <- "Joe"
  isPurple <- TRUE

• Data Types

  carCount <- 2
  age <-15
  seaLevel <- -10000
  usBudget <- 11000000000
  lightSpeed <- 11799312874
  myGPA <- 3.45
  piValue <- 3.14159265
  lastLetter <- "Z"
  isMale <- TRUE
  myName <- "Joe"
  

• Math Op

  carCount <- 6;
  truckCount <- 3;
  
  total <- carCount + truckCount
  print(total)
  
  subtract <- carCount - truckCount
  print(subtract)
  
  multiple <- carCount * truckCount
  print(multiple)
  
  divisible <- carCount / truckCount
  print(divisible)
  
  #  performs division and gets remainder which is 0
  modulo <- carCount %% truckCount
  print(modulo)

• Math Functions

  power <- 3 ^ (6)
  print(power)
  
  root <- sqrt(16)
  print(root)
  
  floorVal <- floor(3.14)
  print(floorVal)
  
  ceilVal <- ceiling(4.3)
  print(ceilVal)
  
  roundVal <- round(3.4)
  print(roundVal)
  
  # random number from 0 to 100
  ranNum <- sample(0:100, 1)
  print(ranNum)

• If/Else

  carCount <- 6;
  
  if (carCount > 3) {
    print("More than three cars");
  } else if(carCount == 3) {
    print("Equal to three cars");
  } else {
    print("Less than three cars");
  }

• Ternary

  carCount <- 3
  
  result = if(carCount > 2) "Yes" else "No"
  print(result)

• Switch

  carCount <- 3
  
  result <- switch(carCount, 
                   "1"="One car", 
                   "2"="Two cars",
                   "3"="Three cars",
                   "More than three")
  print(result)

• Functions

  handleCars <- function(cars, wheels) {
    total <- cars * wheels
    return (total)
  }
  
  result <- handleCars(3, 4)
  print(result)

• Interpolation

  name <- "Joe"
  car <- "Mazda"
  result <- sprintf("%s drvies a %s", name, car)
  print(result)

• Type Casting

  squareA <- function(length) {
    result <- length ^ 2;
    return (as.character(result));
  }
  
  squareL <- "4";
  convertedVal <- as.numeric(squareL);
  area <- squareA(convertedVal);
  print(area)

• Date and Time

  # date and time 
  date = Sys.time()
  print(date)
  
  # epoch time
  milliseconds = as.numeric(as.POSIXct(date))
  print(milliseconds)
  
  # current year
  year = format(date, "%Y")
  print(year)
  
  # current month
  month = format(date, "%m")
  print(month)
  
  # formatted date
  formatted = format(date, "%m/%d/%Y")
  print(formatted)

• Classes

  Cars <- setRefClass("Cars",
    fields = list(carList = "list"),
    methods = list(
      addCar = function(car) {
        carList <<- append(carList, car)
      },
      removeFirst = function() {
        carList <<- carList[-1]
      }
    )
  )
  
  newList <- Cars()
  newList$addCar("Honda")
  newList$addCar("Mazda")
  newList$addCar("Toyota")
  newList$removeFirst()
  
  # direct reference only
  firstCar <- newList$carList[1]
  print(firstCar)

• Inheritance

  User <- setRefClass("User",
    fields = list(
      username = "character",
      password = "character"
    )
  )
  
  Admin <- setRefClass("Admin",
    fields = list(
      id = "character"
    ),
    contains = "User"
  )
  
  newAdmin <- Admin(
    username = "alpha0",
    password = "pw1",
    id = "1FE"
  )
  
  print(newAdmin$username)
  print(newAdmin$id)

• Method Overload

  // No Native Support or Implementation
  

• Abstract Class

  // No Native Support or Implementation
  // Use the R6 library 
  

• Static Class

  // No Native Support or Implementation
  

• Arrays/Lists

  names <- list("Joe", "Alex", "Bob")
  names[2] = "Tom"
  name = names[2]
  numItems = length(names)
  
  print(name)
  print(numItems)

• Array Methods

  cars <- list("Honda", "Mazda", "Toyota")
  
  # number of array elements
  print(length(cars))
  
  # check to see that element is in array
  print("Mazda" %in% cars)
  
  # remove the numbered element
  cars[-1]
  print(cars[1])
  
  # add Ford to array
  append(cars, "Ford")
  print(cars[3])

• Concatenation

  carsListKr <- c("Kia", "Hyundai", "Daewoo")
  carsListJp <- c("Honda", "Mazda", "Toyota")
  combined = cbind(carsListKr, carsListJp)
  
  print(combined[1])
  print(combined[4])

• Sort Method

  ages <- c(5, 3, 1, 6, 7, 4, 19) 
   
  result <- sort(ages) 
  print(result)

• Objects

  User <- setRefClass("User",
    fields = list(
      first = "character",
      last = "character",
      age = "numeric",
      retired = "logical",
      carBrands = "list",
      fullName = "character"
    ),
    methods = list(
      setFullname = function() {
        fullName <<- sprintf("%s %s", first, last)
      }
    )
  )
  
  brands <- list("Mazda", "Toyota");
  
  user <- new("User", 
    first = "Joe",
    last = "Doe",
    age = 23,
    retired = FALSE,
    carBrands = brands
  );
  user$setFullname()
  
  print(user$first)
  print(user$carBrands[1])
  print(user$fullName)

• Maps (Key/Value)

  rm(list = ls())
  # create the list
  carMap <- list()
   
  # Build up key value pairs
  carMap[[ "Joe" ]] <- "Toyota"
  carMap[[ "Bob" ]] <- "Mazda"
  carMap[[ "Tom" ]] <- "Ford"
   
  print(carMap$"Tom")
  
  carMap[["Tom"]] <- NULL
  print(carMap$"Tom" != NULL)

• Sets

  # no built in implementation
  # use external libraries
  

• Stack

  cars <- list()
  cars <- append(cars, "Mazda")
  cars <- append(cars, "Honda")
  cars <- append(cars, "Toyota")
  
  print(cars[length(cars)])
  
  cars <- cars[-length(cars)]
  print(cars[length(cars)])

• Queues

  cars <- list()
  cars <- append(cars, "Mazda")
  cars <- append(cars, "Honda")
  cars <- append(cars, "Toyota")
  
  print(cars[1])
  
  cars <- cars[-1]
  print(cars[1])

• Linked List

  Node <- setRefClass("Node",
    field = c(
      value = "character",
      "next" = "ANY"
    )
  )
  
  LinkedList = setRefClass("LinkedList",
    # allows for assigning values by reference
    field = c(
      head = "ANY"
    ),
    
    methods = list(
      add = function(value) {
        newNode <- Node(
          value = value,
          "next" = NULL
        )
        if (is.null(head)) {
          head <<- newNode
        } else {
          current = head
          
          while (!is.null(current[["next"]])) {
            current = current[["next"]]
          }
          
          current[["next"]] = newNode
        }
      },
      
      traverse = function() {
        current = head
        
        while (!is.null(current)) {
          print(current$value)
          current = current[["next"]]
        }
      }
    )
  )
  
  carList = LinkedList(
    head = NULL
  )
  
  carList$add("Mazda")
  carList$add("Toyota")
  carList$add("Honda")
  carList$traverse()

• Graphs

  rm(list = ls())
  
  Graph <- setRefClass("Graph",
    fields = list(graphMap = "list"),
    methods = list(
      addNode = function(val) {
        graphMap[[val]] <<- list()
      },
      
      addVertices = function (node1, node2) {
        templist <- list()
        if(node1 %in% names(graphMap) == FALSE) {
          graphMap[[node1]] <<- list()
        }
        if(node2 %in% names(graphMap) == FALSE) {
          graphMap[[node2]] <<- list()
        }
        nodeOneArr = graphMap[[node1]]
        nodeTwoArr = graphMap[[node2]]
  
        graphMap[[node1]] <<- append(
          nodeOneArr,
          node2
        )
        graphMap[[node2]] <<- append(
          nodeTwoArr,
          node1
        )
      },
      
      breadthTraverse = function(start) {
        queue <- list(start)
        visited <- list()
        visited[[start]] <- TRUE
        
        while(length(queue) > 0) {
          curVal = queue[1]
          print(curVal)
          queue <- queue[-1]
          tempArr = graphMap[[sprintf("%s", curVal)]]
          for(tempVal in tempArr) {
            if (tempVal %in% names(visited) == FALSE) {
              queue <- append(queue, tempVal)
              visited[[tempVal]] <- TRUE
            }
          }
        }
      },
      depthTraverse = function(start) {
        stack <- list(start)
        visited <- list()
        visited[[start]] = TRUE
        
        while(length(stack) > 0) {
          curVal = stack[length(stack)]
          print(curVal);
          stack <- stack[-length(stack)]
          tempArr = graphMap[[sprintf("%s", curVal)]]
          
          for(tempVal in tempArr) {
            if (tempVal %in% names(visited) == FALSE) {
              stack <- append(stack, tempVal)
              visited[[tempVal]] <- TRUE
            }
          }
        }
      }
    )
  )
  
  newGraph <- Graph()
  newGraph$addNode("a")
  newGraph$addVertices("a", "b")
  newGraph$addVertices("a", "c")
  newGraph$addVertices("b", "d")
  newGraph$addVertices("b", "e")
  newGraph$addVertices("d", "f")
  newGraph$addVertices("d", "g")
  newGraph$addVertices("d", "h")
  newGraph$addVertices("e", "i")
  newGraph$addVertices("e", "j")
  newGraph$breadthTraverse("a")
  newGraph$depthTraverse("a")

• For Loops

  names <- list('Joe', 'Alex', 'Bob');
  
  for (name in names) {
    print(name);
  }

• While Loops

  carList <- list("Mazda", "Toyota", "Honda")
  
  while(length(carList) > 0) {
    print(carList[1])
    carList <- carList[-1]
  }
  
  
  print(length(carList))

• Loop Breaks

  cars <- list('Toyota', 'Honda', 'Mazda')
  i <- 0
  
  for (car in cars) {
    if (car == "Honda") {
      result <- sprintf("Found at index %d", i)
      print(result)
      break
    }
    result <- sprintf("Visited index %d", i)
    print(result)
    i <- i + 1
  }

• Recursion

  getSum <- function(arr) {
    if (length(arr) == 1) {
      return (arr[1])
    } else {
      val <- as.numeric(arr[1])
      arr <- arr[-1]
      secondVal <- getSum(arr)
      return(val + as.numeric(secondVal))   
    }
  }
  
  testArr <- list(1, 2, 4, 5)
  sum <- getSum(testArr)
  print(sum)

• Regex Words

  phrase <- "I am legend"
  pattern <- "\\w+"
  rg <- regexpr(pattern, phrase)
  
  result <- regmatches(phrase, rg)
  print(result)

• Regex Numbers

  phrase <- "I am 23"
  pattern <- "\\d+"
  rg <- regexpr(pattern, phrase)
  
  result <- regmatches(phrase, rg)
  print(result)

• Regex Test

  library(stringr)
  
  phrase <- "Bob Lee"
  pattern <- "Lee"
  result <- str_detect(phrase, pattern)
  
  print(result)

• Regex Characters

  phrase <- "##I am legend##"
  pattern <- "\\#+\\w+"
  rg <- regexpr(pattern, phrase)
  
  result <- regmatches(phrase, rg)
  print(result)