根据r中的正则表达式删除部分字符串

Question

假设我有一个字符串向量,如下所示:

vector<-c("hi, how are you doing?", 
           "what time is it?", 
           "the sky is blue", 
           "hi, how are you doing today? You seem tired.", 
           "walk the dog", 
           "the grass is green", 
           "the sky is blue during the day")

vector
[1] "hi, how are you doing?"                      
[2] "what time is it?"                            
[3] "the sky is blue"                             
[4] "hi, how are you doing today? You seem tired."
[5] "walk the dog"                                
[6] "the grass is green"                          
[7] "the sky is blue during the day" 

如何识别前4个单词匹配的所有条目,然后仅保留最长匹配的字符串？我正在寻找我的结果看起来像以下向量:

vector                    
[1] "what time is it?"                                                        
[2] "hi, how are you doing today? You seem tired."
[3] "walk the dog"                                
[4] "the grass is green"                          
[5] "the sky is blue during the day"                          

理想情况下,我想要一个使用的解决方案,stringr所以我可以将它送入管道.

更新:使用不同值进行稳健性检查:

来自@Wimpel的解决方案非常出色,但正如@Wimpel所指出的那样在所有场景中都不起作用.参见例如:

vector<-c("hi, how are you doing?", 
          "what time is it?", 
          "the sky is blue", 
          "hi, how are you doing today? You seem tired.", 
          "walk the dog", 
          "the grass is green", 
          "the sky is blue during the day", 
          "12/7/2018", 
          "8/12/2018", 
          "9/9/2016 ")

df <- data.frame( text = vector, stringsAsFactors = FALSE ) 
df$group_id <- df %>% group_indices( stringr::word( text, start = 1, end = 4) ) 
df %>%
    mutate( length = str_count( text, " ") + 1,
            row_id = row_number() ) %>%
    group_by( group_id ) %>%
    arrange( -length ) %>%
    slice(1) %>%
    ungroup() %>%
    arrange( row_id ) %>%
    select( text )

1 what time is it?                            
2 hi, how are you doing today? You seem tired.
3 walk the dog                                
4 the grass is green                          
5 the sky is blue during the day  

在上面的示例中,即使日期不匹配,日期也会被删除.

Answer 1

使用更新的样本数据

vec <- c("hi, how are you doing?", 
          "what time is it?", 
          "the sky is blue", 
          "hi, how are you doing today? You seem tired.", 
          "walk the dog", 
          "the grass is green", 
          "the sky is blue during the day", 
          "12/7/2018", 
          "8/12/2018", 
          "9/9/2016")

码

library( tidyverse )

df <- data.frame( text = vec, stringsAsFactors = FALSE ) 
#greate group_indices
df$group_id <- df %>% group_indices( stringr::word( text, start = 1, end = 4) ) 

df %>%
  #create some helping variables
  mutate( length = str_count( text, " ") + 1,
          row_id = row_number() ) %>%
  #now group on id
  group_by( group_id ) %>%
  #arrange by group on length (descending)
  arrange( -length ) %>%
  #keep only the first row (of every group ), also keep all strings shorter than 4 words
  filter( (row_number() == 1L & length >= 4) | length < 4 ) %>%
  ungroup() %>%
  #set back to the original order
  arrange( row_id ) %>%
  select( text )

产量

# # A tibble: 8 x 1
# text                                        
#   <chr>                                       
# 1 what time is it?                            
# 2 hi, how are you doing today? You seem tired.
# 3 walk the dog                                
# 4 the grass is green                          
# 5 the sky is blue during the day              
# 6 12/7/2018                                   
# 7 8/12/2018  
# 8 9/9/2016