如何在ggplot2中为红色曲线的上升段设置不同颜色？

能否将红色CMg(q)曲线的上升段更换为另一种颜色？希望从青色的企业关闭点（x=2）开始改色，以此突出该段为供给曲线。

library("tidyverse")
library("mosaic")
library("ggrepel")
library("fontawesome")

mc_cc<-function(x){3*x^2-8*x+10}
ac_cc<-function(x){x^2-4*x+10+10/x}
atc_cc<-function(x){x^2-4*x+10}

ggplot(data.frame(x=c(0,11)), aes(x=x))+
stat_function(fun=mc_cc, geom="line", size=2, color = "red")+
geom_label(aes(x=4.3,y=mc_cc(4.1)), color = "red", label="CMg(q)", size = 5)+
stat_function(fun=ac_cc, geom="line", size=2, color = "blue")+
geom_label(aes(x=4.6,y=ac_cc(5)), color = "blue", label = "CTMe(q)", size = 5)+
stat_function(fun=atc_cc, geom="line", size=2, color = "deepskyblue")+
geom_label(aes(x=4.6,y=atc_cc(4.5)), color = "deepskyblue", label = "CVMe(q)", size = 5)+
geom_segment(x=0, xend=2, y=6.1, yend=6.1, size=1, linetype="longdash", color = "cyan")+
geom_segment(x=3.3, xend=3.3, y=0, yend=16, size=1, linetype="dotted")+
geom_segment(x=0, xend=3.3, y=16, yend=16, size=1, linetype="dotted")+
geom_segment(x=4, xend=4, y=0, yend=26, size=1, linetype="dotted")+
geom_segment(x=0, xend=4, y=26, yend=26, size=1, linetype="dotted")+
annotate("point", x = 2, y = 6.1, color = "cyan", size = 4) +
annotate("text", x = 2, y = 3.5, label = "Punto de\ncierre de\nla empresa", colour = "deepskyblue", size = 4)+
annotate("text", x = 3.4, y = 20, label = "Curva de Oferta", colour = "darkgreen", size = 6, angle = 63)+
annotate("point", x = 3.3, y = 16, color = "black", size = 4) +
annotate("point", x = 4, y = 26, color = "black", size = 4) +
scale_x_continuous(
                 limits=c(0,5.5),
                 expand=expand_scale(mult=c(0,0.1)))+
scale_y_continuous(
                 limits=c(0,30),
                 expand=expand_scale(mult=c(0,0.1)))+
guides(fill=F)+
labs(
   x = "Producción",
   y = "Precio")+
theme_classic(base_family = "Fira Sans Condensed", base_size=20) +
scale_x_continuous(breaks=c(0,2, 3.3, 4),
                 labels=c(0, expression(""), expression(q["1"]), expression(q["2"])),
                 limits=c(0,5),
                 expand=c(0,0))+
scale_y_continuous(breaks=c(0, 6.1, 16, 26),
                 labels=c(0,expression("P=CVMe"), expression(P["1"]), 
expression(P["2"])),
                 limits=c(0,30),
                 expand=c(0,0))

直接用stat_function无法实现分段颜色，需要先生成CMg曲线的数据集，按x=2（青色点）分段后设置不同颜色。以下是修改后的完整代码：

library("tidyverse")
library("mosaic")
library("ggrepel")
library("fontawesome")

mc_cc<-function(x){3*x^2-8*x+10}
ac_cc<-function(x){x^2-4*x+10+10/x}
atc_cc<-function(x){x^2-4*x+10}

# 生成CMg曲线的分段数据
mc_data <- tibble(
  x = seq(0, 5, length.out = 1000),  # 生成足够多的点保证曲线平滑
  y = mc_cc(x),
  # 按x=2分段，标记供给曲线部分
  segment = ifelse(x >= 2, "supply", "other")
)

ggplot() +
# 绘制分段的CMg曲线，x≥2部分用深绿色（和供给曲线标注颜色一致）
geom_line(data = mc_data, aes(x=x, y=y, color=segment), size=2) +
scale_color_manual(values = c("other" = "red", "supply" = "darkgreen"), guide="none") +
# 其余元素保持原代码样式，修正了原代码中多余的"n"前缀
geom_label(aes(x=4.3,y=mc_cc(4.1)), color = "red", label="CMg(q)", size = 5)+
stat_function(fun=ac_cc, geom="line", size=2, color = "blue")+
geom_label(aes(x=4.6,y=ac_cc(5)), color = "blue", label = "CTMe(q)", size = 5)+
stat_function(fun=atc_cc, geom="line", size=2, color = "deepskyblue")+
geom_label(aes(x=4.6,y=atc_cc(4.5)), color = "deepskyblue", label = "CVMe(q)", size = 5)+
geom_segment(x=0, xend=2, y=6.1, yend=6.1, size=1, linetype="longdash", color = "cyan")+
geom_segment(x=3.3, xend=3.3, y=0, yend=16, size=1, linetype="dotted")+
geom_segment(x=0, xend=3.3, y=16, yend=16, size=1, linetype="dotted")+
geom_segment(x=4, xend=4, y=0, yend=26, size=1, linetype="dotted")+
geom_segment(x=0, xend=4, y=26, yend=26, size=1, linetype="dotted")+
annotate("point", x = 2, y = 6.1, color = "cyan", size = 4) +
annotate("text", x = 2, y = 3.5, label = "Punto de\ncierre de\nla empresa", colour = "deepskyblue", size = 4)+
annotate("text", x = 3.4, y = 20, label = "Curva de Oferta", colour = "darkgreen", size = 6, angle = 63)+
annotate("point", x = 3.3, y = 16, color = "black", size = 4) +
annotate("point", x = 4, y = 26, color = "black", size = 4) +
scale_x_continuous(breaks=c(0,2, 3.3, 4),
                 labels=c(0, expression(""), expression(q["1"]), expression(q["2"])),
                 limits=c(0,5),
                 expand=c(0,0))+
scale_y_continuous(breaks=c(0, 6.1, 16, 26),
                 labels=c(0,expression("P=CVMe"), expression(P["1"]), 
expression(P["2"])),
                 limits=c(0,30),
                 expand=c(0,0))+
guides(fill=F)+
labs(x = "Producción", y = "Precio")+
theme_classic(base_family = "Fira Sans Condensed", base_size=20)

说明 #

• 先生成包含x、y值和分段标识的数据集，确保曲线平滑的同时可以精准控制分段颜色
• 将x≥2的部分设置为深绿色，和图中"Curva de Oferta"的标注颜色统一，突出供给曲线
• 修正了原代码中所有多余的"n"前缀（如ngeom_label改为geom_label），避免运行报错

内容的提问来源于stack exchange，提问作者José