rect 函數用來在一張圖上添加矩形，只需要指定左下角和右上角的坐標的位置，就可以畫出一個矩形
基本用法：
plot(1:5, 1:5, xlim = c(0,6), ylim = c (0,6), type = "n") rect(xleft = 1, ybottom = 1, xright = 5, ytop = 5)
效果圖如下：
xleft, ybottom, xright, ytop 支持一次設置多個值，同時創建多個矩形，用法如下：
plot(1:5, 1:5, xlim = c(0,6), ylim = c (0,6), type = "n") rect(xleft = c(1, 2), ybottom = c(1, 2), xright = c(5, 4), ytop = c(5, 4))
效果圖如下：
參數設置：
border : 設置矩形邊框的顏色，默認為"black"， 支持為多個矩形設置不同的值
代碼示例：
plot(1:5, 1:5, xlim = c(0,6), ylim = c (0,6), type = "n")
rect(xleft = c(1, 2), ybottom = c(1, 2), xright = c(5, 4), ytop = c(5, 4), border = c("red", "blue"))
效果圖如下：
col : 設置矩形的填充色，默認為NULL, 表示無填充色，， 支持為多個矩形設置不同的值
plot(1:5, 1:5, xlim = c(0,6), ylim = c (0,6), type = "n")
rect(xleft = c(1, 2), ybottom = c(1, 2), xright = c(5, 4), ytop = c(5, 4), col = c("pink", "green"))
效果圖如下：
density 和 angle : 搭配使用，設置用線條填充矩形，angle 設置線條的角度，默認為45， density 設置填充線條的密度，數值越大越密集
代碼示例：
par(mfrow = c(1,3)) plot(1:5, 1:5, xlim = c(0,6), ylim = c (0,6), type = "n", main = "density = 1") rect(xleft = 1, ybottom = 1, xright = 5, ytop = 5, angle = 45, density = 1) plot(1:5, 1:5, xlim = c(0,6), ylim = c (0,6), type = "n", main = "density = 3") rect(xleft = 1, ybottom = 1, xright = 5, ytop = 5, angle = 45, density = 2) plot(1:5, 1:5, xlim = c(0,6), ylim = c (0,6), type = "n", main = "density = 4") rect(xleft = 1, ybottom = 1, xright = 5, ytop = 5, angle = 45, density = 3)
效果圖如下：
lwd: 設置矩形所有線條的寬度
代碼示例：
plot(1:5, 1:5, xlim = c(0,6), ylim = c (0,6), type = "n") rect(xleft = 1, ybottom = 1, xright = 5, ytop = 5, angle = 45, density = 2, lwd = 3)
效果圖如下：
lty: 設置矩形所有線條的類型
代碼示例：
plot(1:5, 1:5, xlim = c(0,6), ylim = c (0,6), type = "n") rect(xleft = 1, ybottom = 1, xright = 5, ytop = 5, angle = 45, density = 2, lwd = 2, lty = 3)
效果圖如下：
