geom_smooth中的自定义lm公式 [英] Custom lm formula in geom_smooth

问题描述

我正在处理多面图，并在geom_smooth()

I'm working with faceted plots, and adding lines using the lm method in geom_smooth()

d<-data.frame(n=c(100, 80, 60, 55, 50, 102, 78, 61, 42, 18),
              year=rep(2000:2004, 2), 
              cat=rep(c("a", "b"), each=5))

ggplot(d, aes(year, n, group=cat))+geom_line()+geom_point()+
  facet_wrap(~cat, ncol=1)+
  geom_smooth(method="lm")

我想设置一个函数以在适当的情况下应用多项式.我已经设计了一个功能:

I would like to set up a function to apply a polynomial where appropriate. I've worked up a function:

lm.mod<-function(df){
  m1<-lm(n~year, data=df)
  m2<-lm(n~year+I(year^2), data=df)
  ifelse(AIC(m1)<AIC(m2), "y~x", "y~poly(x, 2)")
}

但是我在应用它时遇到了麻烦.有什么想法或更好的方法来解决这个问题吗?

But I'm having trouble applying it. Any ideas, or better ways to approach this?

推荐答案

不可能通过单个geom_smooth调用来应用不同的平滑函数.这是一个基于数据子集平滑的解决方案:

It's not possible to apply different smooth functions with a single geom_smooth call. Here is a solution which is based on smoothing subsets of data:

首先，创建不带geom_smooth的基础图:

First, create the base plot without geom_smooth:

library(ggplot2)
p <- ggplot(d, aes(year, n, group = cat)) +
       geom_line() +
       geom_point() +
       facet_wrap( ~ cat, ncol = 1)

第二，功能by用于为cat的每个级别(用于构面的变量)创建geom_smooth.此函数返回一个列表.

Second, the function by is used to create a geom_smooth for each level of cat (the variable used for facetting). This function returns a list.

p_smooth <- by(d, d$cat, 
               function(x) geom_smooth(data=x, method = lm, formula = lm.mod(x)))

现在，您可以将geom_smooth的列表添加到基本图中:

Now, you can add the list of geom_smooths to your base plot:

p + p_smooth

该图包括上面板的二阶多项式和下面板的线性平滑:

The plot includes a second-order polynomial for the upper panel and a linear smooth for the lower panel:

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