R 编程/示例会话
< R 编程
本页是 R 编程语言的简介。它展示了如何使用 R 执行非常简单的任务。首先，您需要安装 R（请参阅设置页面）。如果您使用 Windows 或 Mac OS，最简单的解决方案是使用 R 图形用户界面（单击其图标）。如果您使用 Linux，请打开终端并在命令提示符下键入 R。
通常，当您打开 R 时，您会在控制台中看到类似于以下的消息
R version 3.5.1 (2018-07-02) -- "Feather Spray"
Copyright (C) 2018 The R Foundation for Statistical Computing
Platform: x86_64-pc-linux-gnu (64-bit)
R is free software and comes with ABSOLUTELY NO WARRANTY.
You are welcome to redistribute it under certain conditions.
Type 'license()' or 'licence()' for distribution details.
Natural language support but running in an English locale
R is a collaborative project with many contributors.
Type 'contributors()' for more information and
'citation()' on how to cite R or R packages in publications.
Type 'demo()' for some demos, 'help()' for on-line help, or
'help.start()' for an HTML browser interface to help.
Type 'q()' to quit R.
[Workspace loaded from ~/.RData]
>
您可以在尖括号 > 后键入您的代码。
R 可以用作一个简单的计算器，我们可以执行任何简单的计算。
> # Sample Session
> # This is a comment
>
> 2 # print a number
[1] 2
> 2+3 # perform a simple calculation
[1] 5
> log(2) # natural log
[1] 0.6931472
我们还可以使用赋值运算符 <- 存储数字或字符串对象。
> x <- 2 # store an object
> x # print this object
[1] 2
> (x <- 3) # store and print an object
[1] 3
>
> x <- "Hello" # store a string object
> x
[1] "Hello"
我们还可以存储向量.
> Height <- c(168, 177, 177, 177, 178, 172, 165, 171, 178, 170) #store a vector
> Height # print the vector
[1] 168 177 177 177 178 172 165 171 178 170
>
> Height[2] # Print the second component
[1] 177
> Height[2:5] # Print the second, the 3rd, the 4th and 5th component
[1] 177 177 177 178
>
> (obs <- 1:10) # Define a vector as a sequence (1 to 10)
[1] 1 2 3 4 5 6 7 8 9 10
>
> Weight <- c(88, 72, 85, 52, 71, 69, 61, 61, 51, 75)
>
> BMI <- Weight/((Height/100)^2) # Performs a simple calculation using vectors
> BMI
[1] 31.17914 22.98190 27.13141 16.59804 22.40879 23.32342 22.40588 20.86112
[9] 16.09645 25.95156
我们还可以用以下方法描述向量length(), mean()和var().
> length(Height)
[1] 10
> mean(Height) # Compute the sample mean
[1] 173.3
> var(Height)
[1] 22.23333
我们还可以定义一个矩阵.
> M <- cbind(obs,Height,Weight,BMI) # Create a matrix
> typeof(M) # Give the type of the matrix
[1] "double"
> class(M) # Give the class of an object
[1] "matrix"
> is.matrix(M) # Check if M is a matrix
[1] TRUE
> is.vector(M) # M is not a vector
[1] FALSE
> dim(M) # Dimensions of a matrix
[1] 10 4
我们可以使用以下方法绘制数据plot().
> plot(Height,Weight,ylab="Weight",xlab="Height",main="Corpulence")
我们可以定义一个数据框.
> mydat <- data.frame(M) # Creates a dataframe
> names(mydat) # Give the names of each variable
[1] "obs" "Height" "Weight" "BMI"
> str(mydat) # give the structure of your data
'data.frame': 10 obs. of 4 variables:
$ obs : num 1 2 3 4 5 6 7 8 9 10
$ Height: num 168 177 177 177 178 172 165 171 178 170
$ Weight: num 88 72 85 52 71 69 61 61 51 75
$ BMI : num 31.2 23 27.1 16.6 22.4 ...
>
> View(mydat) # Look at your data
>
> summary(mydat) # Descriptive Statistics
obs Height Weight BMI
Min. : 1.00 Min. :165.0 Min. :51.00 Min. :16.10
1st Qu.: 3.25 1st Qu.:170.2 1st Qu.:61.00 1st Qu.:21.25
Median : 5.50 Median :174.5 Median :70.00 Median :22.70
Mean : 5.50 Mean :173.3 Mean :68.50 Mean :22.89
3rd Qu.: 7.75 3rd Qu.:177.0 3rd Qu.:74.25 3rd Qu.:25.29
Max. :10.00 Max. :178.0 Max. :88.00 Max. :31.18
>
您可以保存 R 会话（内存中的所有对象）并加载会话。
> save.image(file="~/Documents/Logiciels/R/test.rda")
> load("~/Documents/Logiciels/R/test.rda")
我们可以定义一个工作目录。注意 Windows 用户：R 在目录中使用斜杠（“/”）而不是反斜杠（“\”）。
> setwd("~/Desktop") # Sets working directory (character string enclosed in "...")
> getwd() # Returns current working directory
[1] "/Users/username/Desktop"
> dir() * Lists the content of the working directory
R 中有一些特殊字符
- NA : 不可用（即缺失值）
- NaN : 非数字（例如 0/0）
- Inf: 无限大
- -Inf : 负无穷大。
例如，0 除以 0 会得到一个NaN但 1 除以 0 会得到
> 0/0
[1] NaN
> 1/0
[1] Inf
我们可以使用以下方法退出 Rq(). 这no参数指定不保存 R 会话。
q("no")