从整数序列生成表达式文字的列表 [英] Generate a list of expression literals from an integer sequence

问题描述

我想将一系列整数映射到一个表达式文字的序列，以便将后者用作图形中的刻度标记标签，例如

I would like to map a sequence of integers to a sequence of expression literals in order to use the latter as tick mark labels in a plot, e.g.

lbls <- lapply(-2:2, function(i) expression(i * pi))
plot(...)
axis(1, at=seq(-2,2)*pi, labels=lbls)

到目前为止，我已经尝试了所有的变体 bquote ，替代，表达式等想想，但显然我一定错过了一些东西。
另外，FAQ和相关的SO问题&答案并没有完全解决这个问题。

So far I've tried all variations of bquote, substitute, expression etc. that I could think of, but apparently I must have missed something. Also, the FAQ and related SO questions & answers didn't fully solve this for me.

如何正确执行（我想要 axis pi 作为希腊字母，并有 -2 ... 2 替代 i 在上面的例子中）？

How would I do it correctly (I want axis to render pi as the greek letter and have -2 ... 2 substituted for i in the above example)?

推荐答案

尝试这个：

lbls <- do.call("expression", lapply(-2:2, function(i) substitute(X * pi, list(X = i))))
plot(-10:10, -10:10, xaxt="n")
axis(1, at=seq(-2,2)*pi, labels=lbls)

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