> lm_sensitivity <- carpenter_dobkin_2009 %>%
+   filter(agecell >= 20 & agecell <= 22) %>%
+   mutate(threshold = ifelse(agecell >= 21, 1, 0)) %$%
+   lm(all ~ threshold + I(agecell - 21) + threshold:I(agecell - 21))
Error in carpenter_dobkin_2009 %>% filter(agecell >= 20 & agecell <= 22) %>%  :
  没有"%$%"这个函数