R語言速成_尹鴻（二）數據類型

數據類型

向量c

一維數據，必須相同類型

> a <- c(1,3,5,7)
> a
[1] 1 3 5 7

#若輸入不同類型，則發生轉化
> a <- c(1,'123')
> a
[1] "1"   "123"

#訪問向量中的值
> a <- c(1,3,5,7)
> a[4]    #並不是像其他語言那樣，索引從0開始
[1] 7
> a[c(1,4)]
[1] 1 7

#切片
> a[1:3]
[1] 1 3 5

矩陣matrix

matrix(data = NA, nrow = 1, ncol = 1, byrow = FALSE, dimnames = NULL)

• nrow—行數
• ncol—列數
• byrow—是否按行進行填充
• dimnames—行名與列名

#創建
> y = matrix(5:24,nrow=4,ncol=5)
> y
     [,1] [,2] [,3] [,4] [,5]
[1,]    5    9   13   17   21
[2,]    6   10   14   18   22
[3,]    7   11   15   19   23
[4,]    8   12   16   20   24

> a <- c(1,3,5,7)
> rnames <- c("R1", "R2")
> cnames <- c("C1", "C2")
> newMatrix <- matrix(a, nrow=2, ncol=2, byrow=TRUE, dimnames=list(rnames,cnames))
> newMatrix
   C1 C2
R1  1  3
R2  5  7

#訪問其中的值
> x <- matrix(1:20, nrow=4, ncol=5)
> x
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    5    9   13   17
[2,]    2    6   10   14   18
[3,]    3    7   11   15   19
[4,]    4    8   12   16   20
> x[3,]
[1]  3  7 11 15 19
> x[2,3]
[1] 10
> x[,4]
[1] 13 14 15 16

數組array

array(data = NA, dim = length(data), dimnames = NULL)

允許多重維度

#創建3x2x4的多維數組
> dim1 <- c("A1", "A2", "A3")
> dim2 <- c("B1", "B2")
> dim3 <- c("C1", "C2", "C3", "C4")
> d <- array(1:24, c(3,2,4), dimnames=list(dim1,dim2,dim3))
> d
, , C1

   B1 B2
A1  1  4
A2  2  5
A3  3  6

, , C2

   B1 B2
A1  7 10
A2  8 11
A3  9 12

, , C3

   B1 B2
A1 13 16
A2 14 17
A3 15 18

, , C4

   B1 B2
A1 19 22
A2 20 23
A3 21 24

> d[1,2,3]    #行，列，維度
[1] 16

數據框data.frame

每一列的類型必須相同
data.frame(…, row.names = NULL, check.rows = FALSE,
check.names = TRUE, fix.empty.names = TRUE,
stringsAsFactors = default.stringsAsFactors())

> ?data.frame
# 生成一個data.frmae
> patientID <- c(1,2,3,4)
> age <- c(25, 34, 28, 52)
> diabetes <- c("Type1", "Type2", "Type3", "Type2")
> status <- c("poor", "Improved", "Excellent", "poor")
> patientsData <- data.frame(patientID, age, diabetes, status)
> patientsData
  patientID age diabetes    status
1         1  25    Type1      poor
2         2  34    Type2  Improved
3         3  28    Type3 Excellent
4         4  52    Type2      poor
# 切片
> patientsData[1:2]
  patientID age
1         1  25
2         2  34
3         3  28
4         4  52
> patientsData[c("diabetes", "status")
+ ]
  diabetes    status
1    Type1      poor
2    Type2  Improved
3    Type3 Excellent
4    Type2      poor
# 利用attach可直接輸入列名顯示該列
> patientsData$age
[1] 25 34 28 52
> attach()
Error in attach() : 缺少參數"what",也沒有缺省值
> age
[1] 25 34 28 52
> head(mtcars)
                   mpg cyl disp  hp drat    wt  qsec vs am gear carb
Mazda RX4         21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
Mazda RX4 Wag     21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
Datsun 710        22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
Hornet 4 Drive    21.4   6  258 110 3.08 3.215 19.44  1  0    3    1
Hornet Sportabout 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2
Valiant           18.1   6  225 105 2.76 3.460 20.22  1  0    3    1
> mpg
錯誤: 找不到對象'mpg'
> attach(mtcars)
> mpg
 [1] 21.0 21.0 22.8 21.4 18.7 18.1 14.3 24.4 22.8 19.2 17.8 16.4 17.3 15.2
[15] 10.4 10.4 14.7 32.4 30.4 33.9 21.5 15.5 15.2 13.3 19.2 27.3 26.0 30.4
[29] 15.8 19.7 15.0 21.4
> detach(mtcars)
> mpg
錯誤: 找不到對象'mpg'
> with(mtcars, {})
NULL
> with(mtcars, {
+ l <- mpg
+ l}
+ )
 [1] 21.0 21.0 22.8 21.4 18.7 18.1 14.3 24.4 22.8 19.2 17.8 16.4 17.3 15.2
[15] 10.4 10.4 14.7 32.4 30.4 33.9 21.5 15.5 15.2 13.3 19.2 27.3 26.0 30.4
[29] 15.8 19.7 15.0 21.4
> diabetes
[1] "Type1" "Type2" "Type3" "Type2"
> diabetes <- factor(diabetes)
> diabetes
[1] Type1 Type2 Type3 Type2
Levels: Type1 Type2 Type3

列表list

不同類型可以結合在一起

> ?list
> g <- "My first list"
> h <- c(12, 45, 43, 90)
> j <- matrix(1:10, nrow=2)
> k <- c("one", "two", "three")
> mylist <- list(g, h, j, k)
> mylist
[[1]]
[1] "My first list"

[[2]]
[1] 12 45 43 90

[[3]]
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    3    5    7    9
[2,]    2    4    6    8   10

[[4]]
[1] "one"   "two"   "three"
#訪問
> mylist[2]
[[1]]
[1] 12 45 43 90