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Question

我想在同一个图上有三个不同参数 alpha 的曲线。

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. 我如何使它正确？

Answer 1

更好的循环答案来自 here和用户 20650。

用 sapply 解决方案
expression功能相当棘手，但与 substitute 一起使用您可以使用 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)