1 Basic Building Blocks

• ?functionname 查看函数详情

？c

• 可以直接把vector和新元素连接起来

> z <- c(1.1, 9, 3.14)
> c(z, 555, z)
[1]   1.10   9.00   3.14 555.00   1.10   9.00   3.14

• vector可以直接参与运算

> z * 2 + 100
[1] 102.20 118.00 106.28

• vector循环运算

> c(1, 2, 3, 4) + c(0, 10)
[1]  1 12  3 14
> c(1, 2, 3, 4) + c(0, 10, 100)
[1]   1  12 103   4
Warning message:
In c(1, 2, 3, 4) + c(0, 10, 100) :
  longer object length is not a multiple of shorter object length

• 按键盘上箭头回溯历史命令

2 Workspace and Files

• getwd() 获取当前工作空间路径
• setwd("dirname") 重设工作空间路径
• ls() 查看工作目录下所有对象
• list.files()或dir() 列出工作目录所有文件
• args(functionname) 查看函数参数
• dir.create("dirname") 新建目录（递归创建：recursive参数要设置为TURE）
• file.create("filename") 新建文件（文件名带后缀）
• file.exists("filename") 检验文件是否存在
• file.info("filename") 获取文件信息
• file.info("filename")$item 获取文件具体某项信息
• file.rename("form_filename", "to_filename") 文件重命名
• file.remove("filename") 删除文件
• file.copy("form_filename", "to_filename") 复制文件
• file.path("filename") 查看相对路径

3 Sequences of Numbers

• :运算符创建数列

> 1:20
 [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20
> pi:10
[1] 3.141593 4.141593 5.141593 6.141593 7.141593 8.141593 9.141593
> 15:1
 [1] 15 14 13 12 11 10  9  8  7  6  5  4  3  2  1
## ，使用 ?`:`查看帮助

• seq() 函数创建数列

> seq(1, 20)
 [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20
> seq(0, 10, by = 0.5)
 [1]  0.0  0.5  1.0  1.5  2.0  2.5  3.0  3.5  4.0  4.5  5.0  5.5  6.0  6.5  7.0  7.5
[17]  8.0  8.5  9.0  9.5 10.0
> my_seq <- seq(5, 10, length = 30)
> 1:length(my_seq)
 [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
[29] 29 30
> seq(along.with = my_seq)
 [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
[29] 29 30
> seq_along(my_seq)
 [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
[29] 29 30

• rep() 函数复制数列

> rep(0, times = 40)
 [1] 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
> rep(c(0, 1, 2), times = 10)
 [1] 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2
> rep(c(0, 1, 2), each = 10)
 [1] 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2

4 Vectors

• 逻辑运算

> num_vect >= 6
[1] FALSE  TRUE FALSE  TRUE

• 字符拼贴与连接

> my_char <- c("My", "name", "is")
> my_name <- c(my_char, "Sylvia")
> my_name
[1] "My"     "name"   "is"     "Sylvia"
> paste(my_name, collapse = " ")
[1] "My name is Sylvia"
> paste("Hello", "world!", sep = " ")
[1] "Hello world!"
> paste(1:3, c("X", "Y", "Z"), sep = "")
[1] "1X" "2Y" "3Z"
> paste(LETTERS, 1:4, sep = "-")
 [1] "A-1" "B-2" "C-3" "D-4" "E-1" "F-2" "G-3" "H-4" "I-1" "J-2" "K-3" "L-4" "M-1" "N-2"
[15] "O-3" "P-4" "Q-1" "R-2" "S-3" "T-4" "U-1" "V-2" "W-3" "X-4" "Y-1" "Z-2"

• sep，collapse，step的区别

> paste(1:10,sep=",")
[1] "1"  "2"  "3"  "4"  "5"  "6"  "7"  "8"  "9"  "10"
> paste(1:10,1,sep=",")
[1] "1,1"  "2,1"  "3,1"  "4,1"  "5,1"  "6,1"  "7,1"  "8,1"  "9,1"  "10,1"
> paste(1:10,collapse=",")
[1] "1,2,3,4,5,6,7,8,9,10"
> paste(1:10,1,collapse=",")
[1] "1 1,2 1,3 1,4 1,5 1,6 1,7 1,8 1,9 1,10 1"
> paste(1:10,step=",")
[1] "1 ,"  "2 ,"  "3 ,"  "4 ,"  "5 ,"  "6 ,"  "7 ,"  "8 ,"  "9 ,"  "10 ,"
> paste(1:10,1,step=",")
[1] "1 1 ,"  "2 1 ,"  "3 1 ,"  "4 1 ,"  "5 1 ,"  "6 1 ,"  "7 1 ,"  "8 1 ,"  "9 1 ,"  "10 1 ,"
> paste(1:10,1)
[1] "1 1"  "2 1"  "3 1"  "4 1"  "5 1"  "6 1"  "7 1"  "8 1"  "9 1"  "10 1"

5 Missing Values

• NA参与运算仍是NA

> x <- c(44, NA, 5, NA)
> x * 3
[1] 132  NA  15  NA

• is.na() 判定是否NA，返回逻辑值（不能使用my_data == NA，因为NA不是一个值）
• sum() 计算值为TRUE的数量

> my_na <- is.na(my_data)
> sum(my_na)
[1] 48

• NaN

> 0 / 0
[1] NaN
> Inf / Inf
[1] NaN
> Inf - Inf
[1] NaN

6 Subsetting Vectors

• R从1开始排序

> x[1:10]
 [1]  1.0368761         NA         NA  1.3890263 -2.6372952         NA         NA
 [8] -0.7592451         NA         NA

• 对vector抽取子集

> x[c(3, 5, 7)]
> x[c(-2, -10)]
> x[-c(2, 10)]

• 对vector取大于零的子集需要先排除缺失值，NA > 0返回NA

> x[x > 0]
 [1] 1.03687611         NA         NA 1.38902626         NA         NA         NA
 [8]         NA         NA         NA         NA 0.03432245 0.35275056 0.72752453
[15]         NA         NA         NA 0.29281794 0.15857674         NA         NA
[22] 1.70880097         NA         NA         NA 0.44062886 0.13357081         NA
[29]         NA         NA
> x[!is.na(x) & x > 0]
 [1] 1.03687611 1.38902626 0.03432245 0.35275056 0.72752453 0.29281794 0.15857674
 [8] 1.70880097 0.44062886 0.13357081

• identical(x, y)判断两个对象是否一致
• names()给对象命名，查看命名

> vect <- c(foo = 11, bar = 2, norf = NA)
> names(vect)
[1] "foo"  "bar"  "norf"
> vect2 <- c(11, 2, NA)
> names(vect2) <- c("foo", "bar", "norf")
> identical(vect, vect2)
[1] TRUE
> vect["bar"]
bar 
  2 
> vect[c("foo", "bar")]
foo bar 
 11   2 

7 Matrices and Data Frames

• dim()返回或设定对象尺寸（vector默认为NULL）
• length()返回对象长度
• class()查看对象种类

> dim(my_vector) <- c(4, 5) 
> attributes(my_vector)  ##另一个查看dim属性的方法
$dim
[1] 4 5
> class(my_vector) 
[1] "matrix"

• matrix()创建矩阵
• cbind()根据列进行合并,合并的前提是所有数据行数相等
• data.frame()创建数据框
• colnames()给数据框定义表头

> my_matrix2 <- matrix(1:20, 4, 5)
my_data <- data.frame(patients, my_matrix)
> cnames <- c("patient", "age", "weight", "bp", "rating", "test")
> colnames(my_data) <- cnames

8 Logic

• &运算符会和vector所有元素比较，&&则只和第一个元素比较