1

下載Package MASS

library(MASS)
dta<-ls("package:MASS") 
dta %>% summary()
##    Length     Class      Mode 
##       165 character character

List the names of the item indices from 94 to 103

dta[94:103]
##  [1] "minn38"            "motors"            "muscle"           
##  [4] "mvrnorm"           "nclass.freq"       "neg.bin"          
##  [7] "negative.binomial" "negexp.SSival"     "newcomb"          
## [10] "nlschools"

2

先把women資料另存到W裡面才能做變動，Height_centered表示把原來的數值檢減去平均數

W<-women
coef(lm(weight ~ height, data = W))
## (Intercept)      height 
##   -87.51667     3.45000
W <- W %>% mutate(height_centered=height-mean(W$height))
knitr::kable(head(W, 10))
height weight height_centered
58 115 -7
59 117 -6
60 120 -5
61 123 -4
62 126 -3
63 129 -2
64 132 -1
65 135 0
66 139 1
67 142 2

用Height_centered來對weight做回歸，結果如下：

coef(lm(weight ~ height_centered, data = W))
##     (Intercept) height_centered 
##        136.7333          3.4500

兩者的截距不一樣是因為我們對x變項做了平移(減去平均數)

3

women本來是data.frame的格式，如果直接用c(women)會讓他變成list

class(women)
## [1] "data.frame"
c(women) %>% class
## [1] "list"
c(women)
## $height
##  [1] 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72
## 
## $weight
##  [1] 115 117 120 123 126 129 132 135 139 142 146 150 154 159 164

如果強制他為matrix，則會讓原本women中屬於height或weight的變項屬性消失，只留下數值

c(as.matrix(women))
##  [1]  58  59  60  61  62  63  64  65  66  67  68  69  70  71  72 115 117
## [18] 120 123 126 129 132 135 139 142 146 150 154 159 164

4

原先birthwt$race的output是integer，會看不出來數字代表的意義

birthwt$race %>% class
## [1] "integer"
birthwt$race
##   [1] 2 3 1 1 1 3 1 3 1 1 3 3 3 3 1 1 2 1 3 1 3 1 1 3 3 1 1 1 2 2 2 1 2 1 2
##  [36] 1 1 1 1 1 2 1 2 1 1 1 1 3 1 3 1 3 1 1 3 3 3 3 3 3 3 3 3 1 3 3 3 3 1 2
##  [71] 1 3 3 2 1 2 1 1 2 1 1 1 3 3 3 3 3 1 1 1 1 3 1 1 1 1 1 1 1 1 1 1 3 1 3
## [106] 2 1 1 1 2 1 3 1 1 1 3 1 3 1 3 1 3 1 1 1 1 1 1 1 1 3 1 2 3 3 3 3 2 3 1
## [141] 1 1 3 3 1 1 2 1 3 3 3 1 1 1 1 3 2 1 2 3 1 3 3 3 2 1 3 3 1 1 2 2 2 3 3
## [176] 1 1 1 1 2 3 3 1 3 1 3 3 2 1

使用help("birthwt")後知道mother’s race (1 = white, 2 = black, 3 = other)， 因此下列程式碼是把數字換成對應的種族字串

c("White", "Black", "Other")[birthwt$race] 
##   [1] "Black" "Other" "White" "White" "White" "Other" "White" "Other"
##   [9] "White" "White" "Other" "Other" "Other" "Other" "White" "White"
##  [17] "Black" "White" "Other" "White" "Other" "White" "White" "Other"
##  [25] "Other" "White" "White" "White" "Black" "Black" "Black" "White"
##  [33] "Black" "White" "Black" "White" "White" "White" "White" "White"
##  [41] "Black" "White" "Black" "White" "White" "White" "White" "Other"
##  [49] "White" "Other" "White" "Other" "White" "White" "Other" "Other"
##  [57] "Other" "Other" "Other" "Other" "Other" "Other" "Other" "White"
##  [65] "Other" "Other" "Other" "Other" "White" "Black" "White" "Other"
##  [73] "Other" "Black" "White" "Black" "White" "White" "Black" "White"
##  [81] "White" "White" "Other" "Other" "Other" "Other" "Other" "White"
##  [89] "White" "White" "White" "Other" "White" "White" "White" "White"
##  [97] "White" "White" "White" "White" "White" "White" "Other" "White"
## [105] "Other" "Black" "White" "White" "White" "Black" "White" "Other"
## [113] "White" "White" "White" "Other" "White" "Other" "White" "Other"
## [121] "White" "Other" "White" "White" "White" "White" "White" "White"
## [129] "White" "White" "Other" "White" "Black" "Other" "Other" "Other"
## [137] "Other" "Black" "Other" "White" "White" "White" "Other" "Other"
## [145] "White" "White" "Black" "White" "Other" "Other" "Other" "White"
## [153] "White" "White" "White" "Other" "Black" "White" "Black" "Other"
## [161] "White" "Other" "Other" "Other" "Black" "White" "Other" "Other"
## [169] "White" "White" "Black" "Black" "Black" "Other" "Other" "White"
## [177] "White" "White" "White" "Black" "Other" "Other" "White" "Other"
## [185] "White" "Other" "Other" "Black" "White"