在 R 中，您将如何编写包装函数或类来将数字格式化为百分比、货币等? [英] How would you write a wrapper function or class to format numbers as percent, currency, etc. in R?

问题描述

在上一个问题中，我询问了基 R 中是否存在方便的包装器来将数字格式化为百分比.

In a previous question, I asked whether whether a convenient wrapper exists inside base R to format numbers as percentages.

这引起了三个回应:

1. 可能不会.
2. 这样的包装器太窄而无用.用户最好学习如何使用现有工具，例如 sprintf，它们可以高度灵活地格式化数字.
3. 无论如何，这样的包装器是有问题的，因为您无法对对象执行计算.

1. Probably not.
2. Such a wrapper would be too narrow to be useful. It is better that useRs learn how to use existing tools, such as sprintf, which can format numbers in a highly flexible way.
3. Such a wrapper is problematic, anyway, since you lose the ability to perform calculations on the object.

不过，在我看来，sprintf 函数对于 R 初学者来说有点过于模糊，无法学习(除非他们来自 C 背景).也许更好的解决方案是修改 format 或 prettyNum 以提供添加前缀和后缀的选项，这样您就可以轻松创建百分比、货币、度数等.

Still, in my view the sprintf function is just a little bit too obfuscated for the R beginner to learn (except if they come from a C background). Perhaps a better solution is to modify format or prettyNum to have options for adding prefixes and suffixes, so you could easily create percents, currencies, degrees, etc.

问题:

您将如何设计一个函数、类或函数集，以优雅地将数字格式化为百分比、货币、度数等?

How would you design a function, class or set of functions to elegantly deal with formatting numbers as percentages, currencies, degrees, etc?

推荐答案

我可能会让事情变得非常简单.format() 通常可用于大多数基本的格式化需求.我会用一个允许任意 prefix 和 suffix 字符串的简单包装器来扩展它.这是一个简单的版本:

I would probably keep things very simple. format() is generally useful for most basic formatting needs. I would extend that with a simple wrapper that allowed arbitrary prefix and suffix strings. Here is a simple version:

formatVal <- function(x, prefix = "", suffix = "", sep = "", collapse = NULL,
                      ...) {
    x <- format(x, ...)
    x <- paste(prefix, x, suffix, sep = sep, collapse = collapse)
    x
}

如果我真的这样做，我可能不会在 formatVal() 的定义中使用 collapse 参数，而是从 中处理它...，但为了说明，我保持上述功能简单.

If I were doing this for real, I would probably not have the collapse argument in the definition of formatVal(), but instead process it out of ..., but for illustration I kept the above function simple.

使用:

set.seed(1)
m <- runif(5)

一些简单的用法示例

> formatVal(m*100, suffix = "%")
[1] "26.55087%" "37.21239%" "57.28534%" "90.82078%" "20.16819%"
> formatVal(m*100, suffix = "%", digits = 2)
[1] "27%" "37%" "57%" "91%" "20%"
> formatVal(m*100, suffix = "%", digits = 2, nsmall = 2)
[1] "26.55%" "37.21%" "57.29%" "90.82%" "20.17%"
> formatVal(m, prefix = "£")
[1] "£0.2655087" "£0.3721239" "£0.5728534" "£0.9082078" "£0.2016819"
> formatVal(m, prefix = "£", digits = 1)
[1] "£0.3" "£0.4" "£0.6" "£0.9" "£0.2"
> formatVal(m, prefix = "£", digits = 1, nsmall = 2)
[1] "£0.27" "£0.37" "£0.57" "£0.91" "£0.20"

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