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前言

本系列是 STATS 782的课程笔记，主要记录使用 R 语言的一些技巧。

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一、R basic

1. R Operator

①：→ 生成数字序列

> 1:50
[1] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
[18] 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
[35] 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

② %% → 取余（求模）

5 %% 2
# 输出结果为 1，因为 5 除以 2 的余数是 1

③ %/% → 整除

7 %/% 3
# 输出结果为 2，因为 7 除以 3 的商是 2.3333，整数部分为 2

2. 变量赋值

3. c() - combine 函数

用于创建一维向量（vector）和组合数据，可以将多个数值、字符或逻辑值组合成一个向量：

① 创建一个数值向量：

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

> num_vector
[1] 1 2 3 4 5

② 组合已有的向量：

vector1 <- c(1, 2, 3)
vector2 <- c(4, 5, 6)
combined_vector <- c(vector1, vector2)

③ The Recycling Rule：
当 c 函数合并的两个向量长度不同时，

First enlarge the shorter vector by recycling its elements, then combine the vectors element by element.

> c(1, 2, 3, 4) + c(1, 2)
[1] 2 4 4 6

4. 对向量的操作

① 截取向量：
R语言中向量的索引从 1 开始，

> vector_total
[1] 1 0 2 4

> vector_total[1]
[1] 1

> vector_total[1:3]
[1] 1 0 2

> vector_total[c(1, 3)]
[1] 1 2

> vector_total[c(-1, -3)]
[1] 0 4

或截取满足条件的向量value：

> x = c(1, 2, 3, 4)
> x[x > 2]
[1] 3 4

② 改变向量 value
先获取向量，再赋值，即可完成修改value，

> vector_total[1:3] <- 0
> vector_total
[1] 0 0 0 4

使用 ifelse 函数修改：

> x = 1:10
> ifelse(x > 5, x, -x)
[1] -1 -2 -3 -4 -5 6 7 8 9 10

5. Special Numerical Values

① Infinity：
0 作为分母时，根据分子的正负值，得到结果正无穷 / 负无穷

> 1 / 0
[1] Inf

> -1 / 0
[1] -Inf

② NaN：
Not a Number，特殊的常量，代表 “Not a Number”（非数值）。NaN 通常是由数学运算的未定义或不可表示结果导致的：

sqrt(-1)  # 对负数开平方根
# 输出结果为 NaN

0 / 0  # 0 除以 0
# 输出结果为 NaN

log(-1)  # 对负数取对数
# 输出结果为 NaN

③ NA：
Not Available，indicate that a value is missing or not available：

# Any arithmetic expression which contains NA will produce NA as a result.
> 1 + sin(NA)
[1] NA

二、 Built-in Functions

1. min, max and range

The functions min and max return the minimum and maximum values contained in any of their arguments, and the function range returns a vector of length 2 containing the minimum and maximum of the values in the arguments.

> max(1:100)
[1] 100
> max(1:100, Inf)
[1] Inf
> range(1:100)
[1] 1 100

2. sum and prod

The functions sum and prod compute the sum and product of all the elements in their arguments.

> sum(1:100)
[1] 5050
> prod(1:10)
[1] 3628800

3. Cumulative Summaries

> cumsum(1:10)
[1] 1 3 6 10 15 21 28 36 45 55
> cumprod(1:6)
[1] 1 2 6 24 120 720
> cummax(1:10)
[1] 1 2 3 4 5 6 7 8 9 10
> cummin(1:10)
[1] 1 1 1 1 1 1 1 1 1 1

4. paste

Strings can be “glued together” by using paste.
默认以空格分隔：

> paste("First", "Second", "Third")
[1] "First Second Third"

> paste("First", "Second", "Third", sep = ":")
[1] "First:Second:Third"

> paste("First", "Second", "Third", sep = "")
[1] "FirstSecondThird"

对向量进行操作：

> paste(s, "element", sep = "-")
[1] "initial-element" "second-element"
[3] "third-element"

> paste(s, collapse = " -> ")
[1] "initial -> second -> third"

5. list（）

The elements of vectors must all be of the same basic type. Lists provide a way of storing things of different types in a single object.

> lst = list(10, "eleven", TRUE)

> lst = list(1:10, "eleven", TRUE)
> lst
[[1]]
 [1]  1  2  3  4  5  6  7  8  9 10

[[2]]
[1] "eleven"

[[3]]
[1] TRUE

6. seq（）

功能与 “：” 类似，但 “：” 步进只能为 1，

> seq(0, 1, by = .1)
[1] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
> seq(0, 1, length = 11)
[1] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
> seq(0, by = .1, length = 11)
[1] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
> seq(to = 1, by = .1, length = 11)
[1] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

7. rep（）

The first argument to rep gives the values to be repeated and the second specifies how many times to repeat them.

> rep(1:4, 3)
[1] 1 2 3 4 1 2 3 4 1 2 3 4

> rep(1:4, c(2, 3, 2, 3))
[1] 1 1 2 2 2 3 3 4 4 4

> rep(c("A", "B", "C"), 3)
[1] "A" "B" "C" "A" "B" "C" "A" "B" "C"

总结

本文回顾了 STATS 782 第一章节的内容，介绍了R语言的基本运算符，数据类型等，以及一些常用的内置函数。