Hauspreis-stratifizieren.Rmd

```{r}
d <- 
d %>% 
  mutate(size_group = case_when(
    livingArea < quantile(livingArea, prob = .25) ~ 1,
    livingArea < quantile(livingArea, prob = .5) ~ 2,   
    livingArea < quantile(livingArea, prob = .75) ~ 3,
    TRUE ~ 4
  ))
```


```{r results='hide'}
m2a <- stan_glm(price ~ bedrooms + size_group, data = d)
```


```{r}
d_m2a <-
  tibble(
    size_group = 1:4,
    intercept = coef(m2a)[1] + size_group * coef(m2a)[3],
    slope = coef(m2a)[2]
  )
```


```{r fig.asp = 0.4, fig.width=7}
size_group_labs <-
  c(`1` = "sehr kleine Häuser (q1)",
    `2` = "eher kleine Häuser (q2)",
    `3` = "eher große Häuser (q3)",
    `4` = "sehr große Häuser (q4)")

d %>% 
  ggplot(aes(x = bedrooms, y = price)) +
  geom_jitter(alpha = .3) +
  geom_abline(data = d_m2a,
              aes(intercept = intercept,
                  slope = slope),
              color = "blue",
              size = 2) +
  facet_wrap(~ size_group, nrow = 1, labeller = as_labeller(size_group_labs)) +
  labs(title = "Hauspreis als Funktion von Zimmerzahl und Quadratmeter",
       caption = "Facetten zeigen Quartile der Variable 'Quadratmeter'")
```