R:为图标题，轴标签或图例创建拉丁/希腊表达式的矢量 [英] R: creating vectors of latin/greek expression for plot titles, axis labels, or legends

问题描述

我想合并拉丁和希腊文本的向量以生成绘图标题，轴标签，图例条目等.我在下面提供了一个简单的示例.我无法弄清楚如何以其本机形式呈现希腊字母.我已经尝试对paste命令使用expression，parse和apply的各种组合，但是对于单个表达式，我无法向量化容易生成混合拉丁/希腊文本的代码(例如，expression("A ("*alpha*")")适用于单个表达式).

I would like to merge vectors of Latin and Greek text to generate plot titles, axis labels, legend entries, etc. I have provided a trivial example below. I cannot figure out how to render the Greek letters in their native form. I have tried various combinations of expression, parse, and apply to the paste command but I have not been able to vectorize the code that readily generates mixed Latin/Greek text for the case of a single expression (e.g., expression("A ("*alpha*")") is suitable in the case of a single expression).

data<-matrix(seq(20),nrow=5,ncol=4,byrow=TRUE)
colnames(data)<-c("A","B","C","D")
greek<-c(" (alpha)"," (beta)"," (gamma)"," (delta)")
matplot(data)
legend(1,max(data),fill=c("black","red","green","blue"),apply(matrix(paste(colnames(data),greek,sep=""),nrow=4,ncol=1),1,expression))

您能否在legend()语句中的apply()语句中为我提供帮助?需要进行一些修改才能产生所需的输出(即A(α)，B(β)，C(γ)，D(δ)).预先感谢.

Could you please help me with the apply() statement within the legend() statement? It requires some modification to produce the desired output (i.e., A (α), B(β), C(γ), D(δ)). Thanks in advance.

推荐答案

这里是一种避免使用parse()的替代方法，它可以与您对@mnel好的答案的第一个评论中提到的示例配合使用:

Here's an alternative that avoids parse(), and works with the example mentioned in your first comment to @mnel's nice answer:

greek <- c("alpha", "beta", "gamma", "delta")
cnames <- paste(LETTERS[1:4], letters[1:4])

legend_expressions <- 
sapply(1:4, function(i) {
    as.expression(substitute(A (B), 
                  list(A = as.name(cnames[i]), B = as.name(greek[i]))))
})

matplot(data)
legend(1,max(data),fill=c("black","red","green","blue"),legend_expressions)

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