如何使用正则表达式或字符串操作拆分复杂的字符串？

Question

我有一个配料表如下：

Ingredients <- "Starch (Corn | Potato | Wheat) | Vegetables (27%) [Pea (23%) (Flakes | Pieces) | Carrot Pieces | Onion Powder | Spinach Powder] | Croutons (10%) (Wheat Flour | Vegetable Oil | Salt | Yeast) | Maltodextrin | Natural Flavours (Contain Milk and Soybeans) | Creamer [Contains Milk | Mineral Salts (339 or 340 | 450 or 451)] | Salt | Mineral Salt (Potassium Chloride) | Sugar | Flavour Enhancer (621) | Vegetable Oil | Bacon Powder (0.5%) | Parsley | Natural Colour (Turmeric) | Burnt Sugar | Food Acid (Lactic) | Pepper Extract"

我想将它们分成变量ingredients 下数据框中的值。

但是我在编写代码时遇到了问题，因为列表中以各种方式使用了分隔符|。所以我想在 | 上拆分，它不包含在方括号 () 或方括号 [] 中。并且真的不知道如何处理这个问题。

也就是说，我们最终会得到一个成分值 Starch (Corn | Potato | Wheat) 和另一个 Vegetables (27%) [Pea (23%) (Flakes | Pieces) | Carrot Pieces | Onion Powder | Spinach Powder] 以及另一个只是 Salt （加上其他成分，但前两个对我来说是更棘手的情况）。

Answer 1

正则表达式修改自this answer。

这个想法是首先将括号（() 和[]）之间的| 字符替换为其他字符（在我的示例中为@）。剩余的 | 字符应该是字符串的真正分隔符。然后使用strsplit拆分|并将@符号替换回|。最后，trims() 删除每个字符串末尾不需要的空格。

library(dplyr)

strsplit(gsub("\|(?=[^()]*\))", "@", Ingredients, perl=TRUE) %>% 
           gsub("\|(?=[^\[\]]*\])", "@", ., perl=TRUE), "\|") %>% 
  unlist() %>% 
  gsub("@", "\|", .) %>% 
  trimws()

 [1] "Starch (Corn | Potato | Wheat)"                                                                
 [2] "Vegetables (27%) [Pea (23%) (Flakes | Pieces) | Carrot Pieces | Onion Powder | Spinach Powder]"
 [3] "Croutons (10%) (Wheat Flour | Vegetable Oil | Salt | Yeast)"                                   
 [4] "Maltodextrin"                                                                                  
 [5] "Natural Flavours (Contain Milk and Soybeans)"                                                  
 [6] "Creamer [Contains Milk | Mineral Salts (339 or 340 | 450 or 451)]"                             
 [7] "Salt"                                                                                          
 [8] "Mineral Salt (Potassium Chloride)"                                                             
 [9] "Sugar"                                                                                         
[10] "Flavour Enhancer (621)"                                                                        
[11] "Vegetable Oil"                                                                                 
[12] "Bacon Powder (0.5%)"                                                                           
[13] "Parsley"                                                                                       
[14] "Natural Colour (Turmeric)"                                                                     
[15] "Burnt Sugar"                                                                                   
[16] "Food Acid (Lactic)"                                                                            
[17] "Pepper Extract" 

Answer 2

您可以使用递归正则表达式：

pat <- r"(([^[]|]*[[(](?:[^[)(]]*(?1)?)+[])])| ([^|]+))"
regmatches(Ingredients, gregexpr(pat, Ingredients, perl = TRUE))

[[1]]
 [1] "Starch (Corn | Potato | Wheat)"                                                                 
 [2] " Vegetables (27%) [Pea (23%) (Flakes | Pieces) | Carrot Pieces | Onion Powder | Spinach Powder]"
 [3] " Croutons (10%) (Wheat Flour | Vegetable Oil | Salt | Yeast)"                                   
 [4] " Maltodextrin "                                                                                 
 [5] " Natural Flavours (Contain Milk and Soybeans)"                                                  
 [6] " Creamer [Contains Milk | Mineral Salts (339 or 340 | 450 or 451)]"                             
 [7] " Salt "                                                                                         
 [8] " Mineral Salt (Potassium Chloride)"                                                             
 [9] " Sugar "                                                                                        
[10] " Flavour Enhancer (621)"                                                                        
[11] " Vegetable Oil "                                                                                
[12] " Bacon Powder (0.5%)"                                                                           
[13] " Parsley "                                                                                      
[14] " Natural Colour (Turmeric)"                                                                     
[15] " Burnt Sugar "                                                                                  
[16] " Food Acid (Lactic)"                                                                            
[17] " Pepper Extract"