類別解釋變數

R 迴歸入門

Richie Cotton

Data Evangelist at DataCamp

魚類資料集

每列代表一尾魚。
資料集中共有 128 列。
共有 4 種魚類。

species	mass_g
Bream	242.0
Perch	5.9
Pike	200.0
Roach	40.0
...	...

視覺化 1 數值與 1 類別變數

library(ggplot2)

ggplot(fish, aes(mass_g)) +
  geom_histogram(bins = 9) +
  facet_wrap(vars(species))

分面長條圖：魚的數量對應重量。每個分面是一種魚：bream、perch、pike、roach。

摘要統計：各魚種的平均質量

fish %>% 
  group_by(species) %>% 
  summarize(mean_mass_g = mean(mass_g))

# A tibble: 4 x 2
  species mean_mass_g
  <chr>         <dbl>
1 Bream          618.
2 Perch          382.
3 Pike           719.
4 Roach          152.

線性迴歸

lm(mass_g ~ species, data = fish)

Call:
lm(formula = mass_g ~ species, data = fish)

Coefficients:
 (Intercept)  speciesPerch   speciesPike  speciesRoach  
       617.8        -235.6         100.9        -465.8

無截距項

lm(mass_g ~ species + 0, data = fish)

Call:
lm(formula = mass_g ~ species + 0, data = fish)

Coefficients:
speciesBream  speciesPerch   speciesPike  speciesRoach  
       617.8         382.2         718.7         152.0

一起來練習吧！

R 迴歸入門