# 普通作图¶

## 光滑曲线¶

x <- 1:10
y <- c(2,4,6,8,7,12,14,16,18,20)
lo <- loess(y~x)
plot(x,y)
lines(predict(lo), col='red', lwd=2)


## Low-Level Graphics¶

Suppose I want to draw the following figure with R, At first, I try to use xaxt option to remove the axis, but the box still remains, just same as the one question in the StackOverflow, and I found a possible solution, directly use

plot.new()


All is well before I tried to add the text $\rho$, if I use

text(0.8, 0, expression(rho), cex = 2)


it is OK, but it is exactly on the axis, not proper, but when I tried smaller $y$-coordinate, such as -0.1, the text cannot appear, which seems out of the figure. I have tried par() parameters, such as mar, but does not work.

Then I have no idea, and do not know how to google it. And even though I want to post an issue in the StackOverflow. But a random reference give me ideas, in which the example saves me,

> plot.new()
> plot.window(xlim=c(0,1), ylim=c(5,10))
> abline(a=6, b=3)
> axis(1)
> axis(2)
> title(main="The Overall Title")
> title(xlab="An x-axis label")
> title(ylab="A y-axis label")
> box()


Then I realized that I should add

plot.window(xlim = c(0, 1), ylim = c(-0.1, 0.9))


## 画图间距¶

• mar 调节单张图的 margin
• oma 调节整张图外部的 margin

## pairs中自定义panel函数¶ my.lower <- function(x,y,...){
points(x, y)
lines(lowess(x, y), col = "red", lwd=2)
}

my.upper <- function(x, y, ...){
cor.val = round(cor(x,y), digits = 3)
if (abs(cor.val) > 0.5){
text(mean(x), mean(y), cor.val, cex = 3)
text(sort(x)[length(x)*0.8], max(y), '***', cex = 4, col = "red")
} else
{
text(mean(x), mean(y), cor.val, cex = 1)
}
}

pairs(iris[1:4], lower.panel =my.lower, upper.panel = my.upper)