R中传说中的希腊字母

Question

我想在同一个图上用不同的参数 alpha 绘制三个曲线。

curve(sin(x), from = 1, to = 3, lty = 1, ylim = c(-1, 1))
curve(sin(2 * x), add = TRUE, lty = 2)    
curve(sin(3 * x), add = TRUE, lty = 3)
legend("topright", legend = expression(paste(alpha, " = ", c(1, 2, 3))), lty = 1:3)

在图例中，我想要 alpha = 1、alpha = 2、alpha = 3 的三行。如何使其正确？

Answer 1

更好的循环答案来自 here 和 user20650。

用sapply解决

expression 函数非常棘手，但结合 substitute 您可以使用 sapply 循环：

curve(sin(x), from = 1, to = 3, lty = 1, ylim = c(-1, 1))
curve(sin(2 * x), add = TRUE, lty = 2)    
curve(sin(3 * x), add = TRUE, lty = 3)
legend("topright",
       legend = sapply(1:3, function(x) as.expression(substitute(alpha == B,
                                                                 list(B = as.name(x))))),
       lty = 1:3)

简单修复

curve(sin(x), from = 1, to = 3, lty = 1, ylim = c(-1, 1))
curve(sin(2 * x), add = TRUE, lty = 2)    
curve(sin(3 * x), add = TRUE, lty = 3)
legend("topright", legend = c(expression(paste(alpha, " = ", 1)),
                              expression(paste(alpha, " = ", 2)),
                              expression(paste(alpha, " = ", 3))), lty = 1:3)

R中传说中的希腊字母

Greek letters in legend in R

r

expression

legend