标题是变量名称时如何将标题添加到ggplot？ [英] How to add a title to a ggplot when the title is a variable name?

问题描述

  + opts（title = expression（Chart chart_title .. 。））
  

但这不是：

  chart_title =foo
 + opts（title = expression（chart_title））
  

也不是：

  chart_title =foo
 + opts（title = chart_title）
  

标题是变量名称时，如何向ggplot添加标题？ / p>

解决方案

正如其他人指出的，您的示例对于变量chart_title是字符串或表达式的情况似乎正常工作。有时候构造标题变量是非常棘手的;例如，如果chart_title使用一些其他变量，并且如果另外使用了一些希腊字符，则简单的 paste（...）不会引起混淆。足够了。要构建这样的标题，你可以使用类似下面的内容：

  foo < -  rnorm（100）$ b $ （粘贴（图号，数字，：，阿尔法，vs，beta，sep =），列表（数字=数字） chart_title< ）
 qplot（foo，foo）+ opts（title = chart_title）
  

在构建标题 bquote（）时会派上用场。程序化标题建设可能是一个混乱的业务; R FAQ 7.13（ http://cran.r-project.org/doc/FAQ/R-FAQ.html ）可以让你开始，但即使这个FAQ基本上告诉你在有疑问时搜索R-Help。

At the end of a ggplot, this works fine:

+ opts(title = expression("Chart chart_title..."))

But this does not:

chart_title = "foo"
+ opts(title = expression(chart_title))

nor this:

chart_title = "foo"
+ opts(title = chart_title)

How can I add a title to a ggplot when the title is a variable name?

解决方案

As others pointed out, your example seems to work fine for the cases where the variable chart_title is a string or an expression. Sometimes it's tricky to construct the title variable; for instance, a confusing scenario might arise if chart_title uses some other variables, and if in addition you are using some greek characters so a simple paste(...) doesn't suffice. To construct a title like that, you could use something like the following:

foo <- rnorm(100)
number <- 1
chart_title <- substitute(paste("Chart no. ",number,": ",alpha," vs ",beta,sep=""), list(number = number))
qplot(foo,foo) + opts(title = chart_title)

Another function that comes in handy when constructing titles is bquote(). Programmatic title construction can be a messy business; R FAQ 7.13 (http://cran.r-project.org/doc/FAQ/R-FAQ.html) can get you started, but even that FAQ basically tells you to search R-Help when in doubt.

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