如何使用 geom_smooth() 计算整个平滑系列并使用 facet_wrap() 显示每个平滑？

Question

在geom_smooth() 的文档中，有一个示例显示如何使用@ 的参数设置将B 样条平滑拟合到tidyverse mpg dataset 的hwy 与displ 列987654323@df=3的函数：

我想重复同样的例子，但不是只计算一个单一的平滑设置为df 参数，我想使用df 值的范围（例如，3 , 5, 7, 9) 来计算一系列平滑，然后使用facet_wrap() 在单独的面板中显示每个平滑（此外，我还想在平滑曲线周围显示灰色阴影置信区间）。但是，我不太清楚应该使用什么语法，或者 ggplot2 是否甚至可以灵活地直接在 geom_smooth() 内部支持这样的计算。

我在下面发布了一个 MWE：

library(tidyverse)
library(splines)

# ---- Preface with optional additional problem context ----

# This fits 4 different B-splines to the "hwy" vs. "displ" columns of the 
# tidyverse "mpg" tibble, with the bs() df parameter set to c(3, 5, 7, 9).
# This is essentially representative of the kind of result I want, except
# that instead of computing it externally and saving the result to a list
# as I've done here, I want to do it automatically inside of geom_smooth().
fitobj <- list()
for(ii in seq(3,9,2)) {
  fitobj[[as.character(ii)]] <- lm(formula = hwy ~ bs(displ, df=ii), data=mpg)
}

# ---- MWE really starts here ----

# Make 4 identical copies of the "mpg" tibble, with an extra column tacked
# onto the right containing values 3, 5, 7, 9
mpg_rep <- NULL
for(ii in seq(3,9,2)) {
    tbl <- mpg
    tbl$splinedf <- ii
    mpg_rep <- bind_rows(mpg_rep, tbl)  
}

# Make a baseline plot; smooths will be appended afterward
plt <- ggplot(mpg_rep, aes(x=displ, y=hwy, group=splinedf)) +
       geom_point() +
       facet_wrap(~splinedf)

# This does _almost_ what I want, except that instead of plotting a different
# smooth in each panel, it plots the same smooth four times redundantly
print(plt + geom_smooth(method = lm, formula = y ~ bs(x, df=3)))

# This looks like it has sort of the right syntax to do what I want, however
# it returns an error message; I guess perhaps because I'm not allowed to
# reference an aesthetic like this inside a formula?
print(plt + geom_smooth(method = lm, formula = y ~ bs(x, df=splinedf)))

这是一个示例输出，看起来几乎与我想要的一样，除了我想要 4 次不同的平滑而不是相同的平滑 4 次：

如何修改 MWE 以使其完全符合我的要求？

Answer 1

您可以lapply() 平滑图层以添加到绘图中，同时提供新的构面变量。

library(ggplot2)

ggplot(mpg, aes(displ, hwy)) +
  geom_point() +
  lapply(c(3,5,7,9), function(i) {
    geom_smooth(
      data = ~ cbind(., facet = i),
      method = lm,
      formula = y ~ splines::bs(x, i)
    )
  }) +
  facet_wrap(vars(facet))

^{由reprex package (v1.0.0) 于 2021-04-21 创建}