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  • 吴裕雄--天生自然 R语言开发学习:高级数据管理(续三)

    #-----------------------------------#
    # R in Action (2nd ed): Chapter 5   #
    # Advanced data management          #
    # requires that the reshape2        #
    # package has been installed        #
    # install.packages("reshape2")      #
    #-----------------------------------#
    
    # Class Roster Dataset
    Student <- c("John Davis","Angela Williams","Bullwinkle Moose",
                 "David Jones","Janice Markhammer",
                 "Cheryl Cushing","Reuven Ytzrhak",
                 "Greg Knox","Joel England","Mary Rayburn")
    math <- c(502, 600, 412, 358, 495, 512, 410, 625, 573, 522)
    science <- c(95, 99, 80, 82, 75, 85, 80, 95, 89, 86)
    english <- c(25, 22, 18, 15, 20, 28, 15, 30, 27, 18)
    roster <- data.frame(Student, math, science, english, 
                         stringsAsFactors=FALSE)
    
    
    # Listing 5.1 - Calculating the mean and standard deviation
    x <- c(1, 2, 3, 4, 5, 6, 7, 8)
    mean(x)
    sd(x)
    n <- length(x)
    meanx <- sum(x)/n
    css <- sum((x - meanx)**2)            
    sdx <- sqrt(css / (n-1))
    meanx
    sdx
    
    
    # Listing 5.2 - Generating pseudo-random numbers from 
    # a uniform distribution
    runif(5)
    runif(5)
    set.seed(1234)                                                     
    runif(5)
    set.seed(1234)                                                      
    runif(5)
    
    
    # Listing 5.3 - Generating data from a multivariate
    # normal distribution
    library(MASS)
    mean <- c(230.7, 146.7, 3.6)                                           
    sigma <- matrix( c(15360.8, 6721.2, -47.1,                              
                       6721.2, 4700.9, -16.5,
                       -47.1,  -16.5,   0.3), nrow=3, ncol=3)
    set.seed(1234)
    mydata <- mvrnorm(500, mean, sigma)                                     
    mydata <- as.data.frame(mydata)                                         
    names(mydata) <- c("y", "x1", "x2")                                       
    dim(mydata)                                                             
    head(mydata, n=10)   
    
    
    # Listing 5.4 - Applying functions to data objects
    a <- 5
    sqrt(a)
    b <- c(1.243, 5.654, 2.99)
    round(b)
    c <- matrix(runif(12), nrow=3)
    c
    log(c)
    mean(c)
    
    
    #  Listing 5.5 - Applying a function to the rows (columns) of a matrix
    mydata <- matrix(rnorm(30), nrow=6)
    mydata
    apply(mydata, 1, mean)     
    apply(mydata, 2, mean) 
    apply(mydata, 2, mean, trim=.4)   
    
    
    # Listing 5.6 - A solution to the learning example
    options(digits=2)
    Student <- c("John Davis", "Angela Williams", "Bullwinkle Moose",
                 "David Jones", "Janice Markhammer", "Cheryl Cushing",
                 "Reuven Ytzrhak", "Greg Knox", "Joel England",
                 "Mary Rayburn")
    Math <- c(502, 600, 412, 358, 495, 512, 410, 625, 573, 522)
    Science <- c(95, 99, 80, 82, 75, 85, 80, 95, 89, 86)
    English <- c(25, 22, 18, 15, 20, 28, 15, 30, 27, 18)
    
    roster <- data.frame(Student, Math, Science, English,
                         stringsAsFactors=FALSE)
    
    z <- scale(roster[,2:4])
    score <- apply(z, 1, mean)
    roster <- cbind(roster, score)
    
    y <- quantile(score, c(.8,.6,.4,.2))
    roster$grade[score >= y[1]] <- "A"
    roster$grade[score < y[1] & score >= y[2]] <- "B"
    roster$grade[score < y[2] & score >= y[3]] <- "C"
    roster$grade[score < y[3] & score >= y[4]] <- "D"
    roster$grade[score < y[4]] <- "F"
    
    name <- strsplit((roster$Student), " ")
    Lastname <- sapply(name, "[", 2)
    Firstname <- sapply(name, "[", 1)
    roster <- cbind(Firstname,Lastname, roster[,-1])
    roster <- roster[order(Lastname,Firstname),]
    
    roster
    
    
    # Listing 5.4 - A switch example
    feelings <- c("sad", "afraid")
    for (i in feelings)
      print(
        switch(i,
               happy  = "I am glad you are happy",
               afraid = "There is nothing to fear",
               sad    = "Cheer up",
               angry  = "Calm down now"
        )
      )
    
    
    # Listing 5.5 - mystats(): a user-written function for 
    # summary statistics
    mystats <- function(x, parametric=TRUE, print=FALSE) {
      if (parametric) {
        center <- mean(x); spread <- sd(x)
      } else {
        center <- median(x); spread <- mad(x)
      }
      if (print & parametric) {
        cat("Mean=", center, "
    ", "SD=", spread, "
    ")
      } else if (print & !parametric) {
        cat("Median=", center, "
    ", "MAD=", spread, "
    ")
      }
      result <- list(center=center, spread=spread)
      return(result)
    }
    
    
    # trying it out
    set.seed(1234)
    x <- rnorm(500) 
    y <- mystats(x)
    y <- mystats(x, parametric=FALSE, print=TRUE)
    
    
    # mydate: a user-written function using switch
    mydate <- function(type="long") {
      switch(type,
             long =  format(Sys.time(), "%A %B %d %Y"), 
             short = format(Sys.time(), "%m-%d-%y"),
             cat(type, "is not a recognized type
    "))
    }
    mydate("long")
    mydate("short")
    mydate()
    mydate("medium")
    
    
    # Listing 5.9 - Transposing a dataset
    cars <- mtcars[1:5, 1:4]      
    cars
    t(cars)
    
    
    # Listing 5.10 - Aggregating data
    options(digits=3)
    attach(mtcars)
    aggdata <-aggregate(mtcars, by=list(cyl,gear), 
                        FUN=mean, na.rm=TRUE)
    aggdata
    
    
    # Using the reshape2 package
    library(reshape2)
    
    # input data
    mydata <- read.table(header=TRUE, sep=" ", text="
    ID Time X1 X2
    1 1 5 6
    1 2 3 5
    2 1 6 1
    2 2 2 4
    ")
    
    # melt data
    md <- melt(mydata, id=c("ID", "Time"))
    
    # reshaping with aggregation
    dcast(md, ID~variable, mean)
    dcast(md, Time~variable, mean)
    dcast(md, ID~Time, mean)
    
    # reshaping without aggregation
    dcast(md, ID+Time~variable)
    dcast(md, ID+variable~Time)
    dcast(md, ID~variable+Time)
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  • 原文地址:https://www.cnblogs.com/tszr/p/11175339.html
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