title 函數用來在一張圖表上添加標題
基本用法：
main 表示主標題，通常位於圖像的上方， sub 表示副標題，位於圖像的下方， xlab 表示x軸的標簽，ylab 表示y軸的標簽
par(oma = c(1, 1, 1, 1)) plot(1:5, 1:5, xlim = c(0,6), ylim = c (0,6), type = "n", xlab = "", ylab = "") box(which = "figure", col = "red", lwd = 2) box(which = "plot", col = "blue", lwd = 2) title(main = "main tilte", sub = "sub title", xlab = "xlab", ylab = "ylab")
效果圖如下：
參數設置：
col : 設置標題的顏色
cex : 設置標題的文字大小
font : 設置標題的文字的格式
以上三個參數可以針對不同的標題分別進行設置，需要注意的是xlab和ylab 不能分開設置，只能是同時設置，對應的參數為 col.lab, col.cex, font.cex
代碼示例：
plot(1:5, 1:5, xlim = c(0,6), ylim = c (0,6), type = "n", xlab = "", ylab = "") title(main = "main tilte", sub = "sub title", xlab = "xlab", ylab = "ylab", col.main = "red", cex.sub = 1.5, col.lab = "blue")
效果圖：
outer : 邏輯值，如果為TRUE, 將標題放到plot area的外邊
代碼示例：
par(oma = c(5, 5, 3, 3)) plot(1:5, 1:5, xlim = c(0,6), ylim = c (0,6), type = "n", xlab = "", ylab = "") box(which = "figure", col = "red", lwd = 2) box(which = "plot", col = "blue", lwd = 2) title(main = "main tilte", sub = "sub title", xlab = "xlab", ylab = "ylab", outer=TRUE)
效果圖如下：
title 中也允許表達式
代碼示例：
plot(1:5, 1:5, xlim = c(0,6), ylim = c (0,6), type = "n", xlab = "", ylab = "") title(main = expression(sqrt(x)), sub = expression(x^2), xlab = "xlab", ylab = "ylab")
效果圖如下：
更多關於表達式的書寫，可以參考plotmath 函數的幫助文檔