### 模板说明：
### ggplot2画多变量折线图，共用x轴


# 一、最原始办法——手动画每条变量折线
library(ggplot2)

dat <- data.frame(
  water_press = c(2, 4, 6),
  out_volumn = c(1.5, 4, 6),
  in_volumn = c(1, 3, 5)
)

pdf("Dr.Liang.pdf", width = 7, height = 5, family = "GB1")
ggplot(dat) +
  theme_classic() +
  geom_point(aes(x = water_press, y = out_volumn, col = "c")) +
  geom_line(aes(x = water_press, y = out_volumn, col = "c")) +
  geom_point(aes(x = water_press, y = in_volumn, col = "d")) +
  geom_line(aes(x = water_press, y = in_volumn, col = "d")) +
  ggtitle("Dr.Liang 的病生实验") +
  xlab("水检压计") +
  ylab("容积变化") +
  #手动设置图例
  scale_color_manual(
    values = c("c" = "#000080", "d" = "#df6100"),
    name = "变量",
    labels = c("充气容积", "抽气容积")
  )
dev.off()


# 二、将dataFrame变为长数据形式后再绘制