library(MASS)
ls("package:MASS")[94:103]
## [1] "minn38" "motors" "muscle"
## [4] "mvrnorm" "nclass.freq" "neg.bin"
## [7] "negative.binomial" "negexp.SSival" "newcomb"
## [10] "nlschools"
dta <- women
dta$height_centered <- with(height-mean(height),data=dta)
coef(lm(weight ~ height, data = dta))
## (Intercept) height
## -87.51667 3.45000
coef(lm(weight ~ height_centered, data = dta))
## (Intercept) height_centered
## 136.7333 3.4500
模型只是平移改變截距,並不會影響到斜率。
height&weight為兩個不同的data frame
c(women)
## $height
## [1] 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72
##
## $weight
## [1] 115 117 120 123 126 129 132 135 139 142 146 150 154 159 164
height&weight合併為一個一維矩陣
c(as.matrix(women))
## [1] 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 115 117
## [18] 120 123 126 129 132 135 139 142 146 150 154 159 164
head(birthwt)
## low age lwt race smoke ptl ht ui ftv bwt
## 85 0 19 182 2 0 0 0 1 0 2523
## 86 0 33 155 3 0 0 0 0 3 2551
## 87 0 20 105 1 1 0 0 0 1 2557
## 88 0 21 108 1 1 0 0 1 2 2594
## 89 0 18 107 1 1 0 0 1 0 2600
## 91 0 21 124 3 0 0 0 0 0 2622
c("White", "Black", "Other")[birthwt$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"
提取出種族變相項並將代號數字1、2、3改為文字white、Black、other。