dataframe - DataFrames.jl 中 "r"之前的 "..."的用途是什么

Question

我注意到人们使用 r".."。它是做什么用的？谢谢

Answer 1

r"..." 是用于定义 regular expression 的 Julia 语法, 并且在需要正则表达式时在整个语言中使用(而不仅仅是在数据框中)。您可以通过在 Julia REPL 的内置帮助中搜索 r"" 来找到有关此语法的更多信息:

help?> r""
  @r_str -> Regex

  Construct a regex, such as r"^[a-z]*$", without interpolation and unescaping (except
  for quotation mark " which still has to be escaped). The regex also accepts one or
  more flags, listed after the ending quote, to change its behaviour:

    •  i enables case-insensitive matching

    •  m treats the ^ and $ tokens as matching the start and end of individual
       lines, as opposed to the whole string.

    •  s allows the . modifier to match newlines.

    •  x enables "comment mode": whitespace is enabled except when escaped with \,
       and # is treated as starting a comment.

    •  a disables UCP mode (enables ASCII mode). By default \B, \b, \D, \d, \S, \s,
       \W, \w, etc. match based on Unicode character properties. With this option,
       these sequences only match ASCII characters.

  See Regex if interpolation is needed.

  Examples
  ≡≡≡≡≡≡≡≡≡≡

  julia> match(r"a+.*b+.*?d$"ism, "Goodbye,\nOh, angry,\nBad world\n")
  RegexMatch("angry,\nBad world")

  This regex has the first three flags enabled.

更广泛地说，紧接在引文之前/与引文并列的某个单词或字母的模式称为 string macro (或非标准字符串文字)，您甚至可以定义自己的(如在 this 等包中)。 r"..." 语法恰好是内置的，专门用于定义正则表达式对象，这些对象以后可以通过 等函数应用于一个或多个字符串匹配和替换。