如何使用 R 在一个 plot 上叠加 3 个功能

Question

I have three functions and a plot code:

f1 <- function(c){0.187*c-0.000236*c^2+0.194*10-0.00330*100-0.000406*10}
f2 <- function(c){0.187*c-0.000236*c^2+0.194*16.53-0.00330*(16.53^2)-0.000406*16.53}
f3 <- function(c){0.187*c-0.000236*c^2+0.194*20-0.00330*400-0.000406*20}

I wish to plot all three of these on the same graph. I currently have:

png("figure.png")
plot(f1(1:1000), type="l", xlab="x", ylab="y", main="the plot :)")
plot(f2(1:1000), type="l", xlab="x", ylab="y", add = T)
dev.off()

So far this produces just f1 on a plot as opposed to f1 and f2 . I believe I am taking the wrong approach because I am producing another plot and trying to add it to a pre-existing plot. I am unsure whether to use geom_line or something similar and just overlay it.

Is there a straight forward way to plot multiple functions and overlay them in the same plot?

Answer 1

geom_line is for ggplot2 , which is an entirely different plotting system.

If you start with plot() , you can use lines() to draw lines on your current plot. Your lines are pretty close together, so it doesn't matter much here, but with base plot you usually want to calculate the maximum range in advance so your can set your plot window up right from the start:

x = 1:1000
y1 = f1(x)
y2 = f2(x)
y3 = f3(x)

y_range = range(c(y1, y2, y3))

plot(x, y1, ylim = y_range, type="l", xlab="x", ylab="y", main="the plot :)", col = "red")
lines(x, y2, col = "blue")
lines(x, y3, col = "chartreuse")

ggplot2 is made to work with data in data frames - particularly long-format data frames. Here's how we might approach the problem with ggplot . (Note that, unlike above, ggplot calculates the plot limits and gives a nice legend automatically.)

library(ggplot2)
dd = data.frame(x, y1, y2, y3)
d_long = reshape2::melt(data = dd, id.vars = "x", variable.name = "fun", value.name = "y")
ggplot(d_long, aes(x = x, y = y, color = fun)) +
  geom_line()

Answer 2

OR sticking with base R plotting like your code, you can just add the extra functions using lines

plot(f1(1:1000), type="l", xlab="x", ylab="y", main="the plot :)")
lines(1:1000, f2(1:1000))
lines(1:1000, f3(1:1000))

Answer 3

If you want two plots one right next to the other, you have to set the parameter of your palette. Use par(mfrow=c(1,2)) after the png() command.

png("figure.png")
par(mfrow=c(1,2))
plot(f1(1:1000), type="l", xlab="x", ylab="y", main="the plot :)")
plot(f2(1:1000), type="l", xlab="x", ylab="y", add = T)
dev.off()

Answer 4

For functions you can also use curve :

f1 <- function(c){0.187*c-0.000236*c^2+0.194*10-0.00330*100-0.000406*10}
f2 <- function(c){0.187*c-0.000236*c^2+0.194*16.53-0.00330*(16.53^2)-0.000406*16.53}
f3 <- function(c){0.187*c-0.000236*c^2+0.194*20-0.00330*400-0.000406*20}

c0 <- 1
c <- 1000
curve(f1, c0, c, main = 'the plot :)', xlab = 'x', ylab = 'y')
curve(f2, c0, c, add = T)
curve(f3, c0, c, add = T)

As @Gregor noted, geom_line() is a ggplot() call. To go all into the tidyverse , you can do:

#or with ggplot / geom_line
library(tidyverse)

map_df(list(f1 =f1,f2 =  f2,f3 = f3), exec, 1:1000)%>%
  mutate(x = 1:1000)%>%
  gather(key = fx,value = value, -x)%>%
  ggplot(aes(x = x, y = value, col = fx)) + geom_line() 

Finally, you may be interested in facet_grid as well:

map_df(list(f1 =f1,f2 =  f2,f3 = f3), exec, 1:1000)%>%
  mutate(x = 1:1000)%>%
  gather(key = fx,value = value, -x)%>%
  ggplot(aes(x = x, y = value)) + geom_line() +
  facet_grid(rows = vars(fx))