当“add = TRUE"时，curve() 不会向我的绘图添加曲线； [英] curve() does not add curve to my plot when "add = TRUE"

问题描述

我有一个非常简单的问题，我似乎无法弄清楚.我想在一张图中绘制两个方程.我试过 add = TRUE 但这似乎不起作用.

I have a very simple problem that I can't seem to figure out. I want to plot two equations in one graph. I've tried add = TRUE but this doesn't seem to work.

curve(0.044*x+1.638)
curve(0.3438*x+0.5155, add=TRUE)

推荐答案

嗯，实际上，curve 确实有效，但你看不到它.为了解释这一点，我们添加了几行代码:

Well, actually, the curve does work, but you can not see it. To explain this, we add a few more lines of code:

f1 <- function(x) 0.044*x+1.638
f2 <- function(x) 0.3438*x+0.5155
x0 <- seq(0, 1, by = 0.1)

我已经通过 f1 和 f2 定义了您的示例函数.我还在 [0,1] 之间取了 11 个采样点来评估和绘制.为什么是这个范围?因为没有通过参数from、to(见?curve)的指定，curve 将在这个范围内作图.

I have defined your example functions by f1 and f2. I also take 11 sampling points between [0,1] to evaluate and plot. Why this range? Because without specification via arguments from, to (see ?curve), curve will make plot on this range.

现在，让我们看看这个:

Now, let's see this:

>f1(x0)
[1] 1.6380 1.6424 1.6468 1.6512 1.6556 1.6600 1.6644 1.6688 1.6732 1.6776
[11] 1.6820
 > f2(x0)
[1] 0.51550 0.54988 0.58426 0.61864 0.65302 0.68740 0.72178 0.75616 0.79054
[10] 0.82492 0.85930

f1 的函数值远高于 f2.当你第一次调用curve绘制f1时，它会修正ylim大致显示到f1(x).因此，当你添加f2(x)时，在这个ylim中是看不到的.

The function value of f1 is so much higher than f2. When you call curve for the first time to plot f1, it will fix the ylim to show roughly to the range of f1(x). Therefore, when you add f2(x), it will not be seen in this ylim.

试试这个，首先选择一个共享的ylim:

Try this instead, by first choosing a shared ylim:

ylim <- range(c(f1(x0), f2(x0)))
curve(f1, ylim = ylim)
curve(f2, add=TRUE, col = "red")

这类问题是一个常见的陷阱.当你决定在一个图形上绘制多个对象时，你需要设置适当的xlim和ylim 足够容纳所有对象.不要指望 R 会即时"调整这些；它不能这样做.绘制范围在绘制第一幅图时确定.

This kind of problem is a common pitfall. When you decide to plot several objects on a single graph, you need to set the appropriate xlim and ylim that's large enough to hold all objects. Don't expect R to adjust these "on the fly"; it can not do this. Plotting range is determined when the first plot is made.

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