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 绘制三条曲线。

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，我想要三行 alplha = 1, alpha = 2, alpha = 3。如何使它正确？

Answer 1

更好的循环答案来自here 和 user20650。

使用 sapply 的解决方案

expression 函数相当棘手，但结合substitute 你可以使用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)