如何在每个面板中使用不同的截距在多面板图中添加固定斜率线

Question

我使用ggplot2生成一个多面板图（需要ggplot2包）。十个面板中的每一个代表不同的植物生长形式。我需要在每个面板中绘制一条线，其斜率为0.704。但是，每个面板的截距应该不同，例如“fern”为-7.9，“fern ally”为-7.31等。目前，我使用下面的代码生成斜率和截距均为每个小组都一样：

ggplot(veg, aes(x=ord1, y=log(lai+0.000019))) +    
scale_x_discrete(limits=c("1","2","3","4","5","6","7","8","9")) +
scale_y_continuous(limits=c(-12,3)) +
geom_point(shape=1) +
geom_segment(aes(x = 1, xend = 9, y = -8.32 + .704, yend = -8.32 + .704*9), 
           col = "black", size = 1, lty="longdash", lwd=1) +
facet_wrap( ~ plant_growth_form, ncol=5) 

如何在ggplot2中修改此代码，为每个增长表单指定不同的拦截？

使用dput（）生成的可重现数据子集可在以下位置找到：How to compute standard errors for predicted data

Answer 1

首先，创建一个单独的数据框，包含截距和斜率。例如“a”是截距，“b”是斜率。我们将此数据框称为“df3”。

df3 <- data.frame(plant_growth_form = unique(veg[,3]),
                  a = c(-10,-9,-8,-7,-6,-5,-4,-3,-2,-1), # assigned arbitrarily
                  b= 0.704)

#     plant_growth_form   a     b
# 1                herb -10 0.704
# 2                moss  -9 0.704
# 3       woody climber  -8 0.704
# 4        tree sapling  -7 0.704
# 5                fern  -6 0.704
# 6  herbaceous climber  -5 0.704
# 7               undet  -4 0.704
# 8    herbaceous shrub  -3 0.704
# 9               grass  -2 0.704
# 10        woody shrub  -1 0.704

绘制

ggplot(veg, aes(x=ord1, y=log(lai+0.000019))) +    
  scale_x_discrete(limits=c("1","2","3","4","5","6","7","8","9")) +
  scale_y_continuous(limits=c(-12,3)) +
  geom_point(shape=1) +
  geom_abline(aes(intercept=a, slope=b), data=df3) +
  facet_wrap( ~ plant_growth_form, ncol=5)

根据@ aosmith的评论更新调整。

# you could separately modify the dataframe of intercepts & slope, or
# adjust directly in the code below for small data (see <--)
df3 <- data.frame(plant_growth_form = unique(veg[,3]),
                  a = c(-10,-9,-8,-7,-6,-5,-4,-3,-2,-1),  # <-- here
                  b= 0.704)                               # <-- here

# to add the code of extra segment (see <--), in red.
ggplot(veg, aes(x=ord1, y=log(lai+0.000019))) +    
  scale_x_discrete(limits=c("1","2","3","4","5","6","7","8","9")) +
  scale_y_continuous(limits=c(-12,3)) +
  geom_point(shape=1) +
  #geom_abline(aes(intercept=a, slope=b), data=df3) +
  geom_segment(data = df3, aes(x = 1, xend = 9, y = a + b, yend = a + b*9)) +
  geom_segment(aes(x = 1, xend = 9, y = -8.32 + .704, yend = -8.32 + .704*9), # <-- here
               col = "red", size = 1, lty="longdash", lwd=1) +
  facet_wrap( ~ plant_growth_form, ncol=5)