提取字符串中的前导数字,但长度会变化。

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英文:

Extract leading numbers from string, but length varies R

问题

有一列包含字母和数字的字符字符串。该字符串始终以一个或两个数字开头,然后是多个字符。我尝试根据第一个字符的位置将字符串分开。

    have <-
      tribble(
        ~string,
        '12main',
        '6six',
        '42go',
        '5to9'
      )
    
    want <- 
      tribble(
        ~prefix, ~rest,
        '12', 'main',
        '6', 'six',
        '42', 'go',
        '5', 'to9'
      )

我确定有一个使用 `separate` 函数的正则表达式解决方案,但我在使其工作方面遇到了困难。

    want <-
      have %>%
      separate(string,
               into = c('prefix', 'rest'),
               sep = "(?=[0-9])(?<=[a-zA-Z])")
英文:

I have a column which contains a character string containing letters and numbers. The string always starts with one or two numbers, followed by multiple characters. I am trying to separate the string based on where that first character is.

have &lt;-
  tribble(
    ~string,
    &#39;12main&#39;,
    &#39;6six&#39;,
    &#39;42go&#39;,
    &#39;5to9&#39;
  )

want &lt;- 
  tribble(
    ~prefix, ~rest,
    &#39;12&#39;, &#39;main&#39;,
    &#39;6&#39;, &#39;six&#39;,
    &#39;42&#39;, &#39;go&#39;,
    &#39;5&#39;, &#39;to9&#39;
  )

I'm sure there is a regex with separate solution but having trouble getting it working.

want &lt;-
  have %&gt;%
  separate(string,
           into = c(&#39;prefix&#39;, &#39;rest&#39;),
           sep = &quot;(?=[0-9])(?&lt;=[a-zA-Z])&quot;)

答案1

得分: 2

你几乎就要成功了,我们可以通过一个向前查找(用于数字)和一个向后查找(用于非数字)来实现它:

have %&gt;%
  separate(string, sep = &quot;(?&lt;=[0-9])(?=[^0-9])&quot;, into = c(&quot;prefix&quot;, &quot;rest&quot;))
# # A tibble: 4 &#215; 2
#   prefix rest 
#   &lt;chr&gt;  &lt;chr&gt;
# 1 12     main 
# 2 6      six  
# 3 42     go   
# 4 5      to9  

我认为你把查找方向搞反了:?&lt;= 是用于前面的字符串(应该与 [0-9] 一起使用),而 ?= 是用于后面的字符串(应该与 [^0-9][A-Za-z] 一起使用)。

个人觉得这有点有趣:我们基于零长度的模式拆分字符串:前面是数字,后面是非数字,所以拆分实际上是零长度的。

顺便说一下,如果字符串中有两个这样的位置,比如 5to9to5,会出现警告:

have &lt;- structure(list(string = c(&quot;12main&quot;, &quot;6six&quot;, &quot;42go&quot;, &quot;5to9&quot;, &quot;5to9to5&quot;)), class = c(&quot;tbl_df&quot;, &quot;tbl&quot;, &quot;data.frame&quot;), row.names = c(NA, -5L))
have
# # A tibble: 5 &#215; 1
#   string 
#   &lt;chr&gt;  
# 1 12main 
# 2 6six   
# 3 42go   
# 4 5to9   
# 5 5to9to5
have %&gt;%
  separate(string, sep = &quot;(?&lt;=[0-9])(?=[^0-9])&quot;, into = c(&quot;prefix&quot;, &quot;rest&quot;))
# Warning: Expected 2 pieces. Additional pieces discarded in 1 rows [5].
# # A tibble: 5 &#215; 2
#   prefix rest 
#   &lt;chr&gt;  &lt;chr&gt;
# 1 12     main 
# 2 6      six  
# 3 42     go   
# 4 5      to9  
# 5 5      to9  

这是一个警告,说明你正在丢弃一些信息,你可以自行决定是否需要处理这种情况。

另一个选择,因为你在实际数据中有 5to9to5

have %&gt;%
  mutate(strcapture(&quot;^([0-9]+)([^0-9].*)&quot;, string, list(prefix=&quot;&quot;, rest=&quot;&quot;)))
# # A tibble: 5 &#215; 3
#   string  prefix rest  
#   &lt;chr&gt;   &lt;chr&gt;  &lt;chr&gt; 
# 1 12main  12     main  
# 2 6six    6      six   
# 3 42go    42     go    
# 4 5to9    5      to9   
# 5 5to9to5 5      to9to5

现在你可以移除 string

另一个注意事项:如果你打算将 prefix 转换为整数或数字,那么你可以通过使用 list(prefix=0L, rest=&quot;&quot;)(或只是 =0)来避免这种需要。那就是 proto= 参数,虽然它的 data 被丢弃了,但它被用于结果列的名称和目标类。

英文:

You were close, we can achieve it with one look-behind (for a number) and one look-ahead (for a non-number):

have %&gt;%
  separate(string, sep = &quot;(?&lt;=[0-9])(?=[^0-9])&quot;, into = c(&quot;prefix&quot;, &quot;rest&quot;))
# # A tibble: 4 &#215; 2
#   prefix rest 
#   &lt;chr&gt;  &lt;chr&gt;
# 1 12     main 
# 2 6      six  
# 3 42     go   
# 4 5      to9  

I think you had the look-around reversed: ?&lt;= is for preceding string (should be used with [0-9]), and ?= is for following string (should be used with [^0-9] or [A-Za-z]).

Personally I find this a bit intriguing: we are splitting strings based on a 0-length pattern: there is nothing between where the previous is a number and the following is a non-number, so the split is effectively 0-length.

FYI, this does run into warnings if there are two such places in a string, such as 5to9to5:

have &lt;- structure(list(string = c(&quot;12main&quot;, &quot;6six&quot;, &quot;42go&quot;, &quot;5to9&quot;, &quot;5to9to5&quot;)), class = c(&quot;tbl_df&quot;, &quot;tbl&quot;, &quot;data.frame&quot;), row.names = c(NA, -5L))
have
# # A tibble: 5 &#215; 1
#   string 
#   &lt;chr&gt;  
# 1 12main 
# 2 6six   
# 3 42go   
# 4 5to9   
# 5 5to9to5
have %&gt;%
  separate(string, sep = &quot;(?&lt;=[0-9])(?=[^0-9])&quot;, into = c(&quot;prefix&quot;, &quot;rest&quot;))
# Warning: Expected 2 pieces. Additional pieces discarded in 1 rows [5].
# # A tibble: 5 &#215; 2
#   prefix rest 
#   &lt;chr&gt;  &lt;chr&gt;
# 1 12     main 
# 2 6      six  
# 3 42     go   
# 4 5      to9  
# 5 5      to9  

It's a warning that you are discarding some information, over to you if you want/need to guard against this.

An alternative, since you have 5to9to5 in your real data:

have %&gt;%
  mutate(strcapture(&quot;^([0-9]+)([^0-9].*)&quot;, string, list(prefix=&quot;&quot;, rest=&quot;&quot;)))
# # A tibble: 5 &#215; 3
#   string  prefix rest  
#   &lt;chr&gt;   &lt;chr&gt;  &lt;chr&gt; 
# 1 12main  12     main  
# 2 6six    6      six   
# 3 42go    42     go    
# 4 5to9    5      to9   
# 5 5to9to5 5      to9to5

where you can now remove string if you want.

Another note: if you are intending to convert prefix into an integer or a number, then you can preclude that need by using list(prefix=0L, rest=&quot;&quot;) (or just =0) instead. That's the proto= argument, and while its data is discarded, it is used for its names and target classes for each resulting column).

答案2

得分: 1

你也可以使用 extract

有 %&gt;% 
     提取(string, c(&#39;prefix&#39;, &#39;rest&#39;), &quot;(\\d+)(.*)&quot;)

# 一个数据框: 4 &#215; 2
  前缀   剩余 
  &lt;chr&gt;  &lt;chr&gt;
1 12     主要 
2 6      六  
3 42     去   
4 5      到9  
英文:

You can also use extract

have %&gt;%
     extract(string, c(&#39;prefix&#39;, &#39;rest&#39;), &quot;(\\d+)(.*)&quot;)

# A tibble: 4 &#215; 2
  prefix rest 
  &lt;chr&gt;  &lt;chr&gt;
1 12     main 
2 6      six  
3 42     go   
4 5      to9  

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  • 本文由 发表于 2023年4月20日 02:12:17
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