在R中如何筛选数据框某列字符串以指定单词开头的行

实现指定字段筛选的代码如下：

dfUSARating <- dfUSAMovies[, c("rowNum","title", "genre", "rating", "vote")]

你当前使用的str_detect全局包含匹配，会把所有多类型组合中带有Thriller的条目全部筛选出来，不符合你仅要首位类型为Thriller的需求：

thrill <- dfUSARating %>% filter(str_detect(dfUSARating$genre, "Thriller"))
# 前3条genre字段示例输出
head(dfUSARating$genre, n=3) 
[1] ['Documentary', 'Comedy', 'Drama', 'Fantasy', 'Mystery', 'Sci-Fi']
[2] ['Comedy', 'Horror', 'Sci-Fi']                                    
[3] ['Biography', 'Drama', 'Sport']  

修改正则匹配规则，用^锚定字符串开头，仅匹配genre字段首个类型为Thriller的条目即可：

thrill_first <- dfUSARating %>% 
  filter(str_detect(as.character(genre), "^\\['Thriller"))

说明：因为你的genre字段为factor类型，先转成character再做匹配可以避免因子level带来的匹配异常问题

dput(head(dfUSARating))
structure(list(rowNum = c(6L, 7L, 8L, 12L, 13L, 15L), genre = 
structure(c(869L, 
752L, 638L, 130L, 229L, 910L), .Label = c("['Action', 
'Adventure', 'Animation', 'Comedy']", 
"['Action', 'Adventure', 'Biography', 'Drama', 'History', 
'War']", 
"['Action', 'Adventure', 'Biography', 'Drama', 'History']", " 
 ['Action', 'Adventure', 'Biography', 'History', 'Romance']", 
"['Action', 'Adventure', 'Biography', 'History']", "['Action', 
'Adventure', 'Comedy', 'Crime', 'Drama', 'Thriller']", 
"['Comedy', 'Drama', 'Mystery']", "['Comedy', 'Drama', 'Romance', 
'Fantasy']", 
"['Comedy', 'Drama', 'Romance', 'Sci-Fi']", "['Comedy', 'Drama', 
'Romance', 'Sport']", 
"['Comedy', 'Drama', 'Romance', 'Thriller']", "['Comedy', 
'Drama', 'Romance', 'War']", 
"['Comedy', 'Drama', 'Romance', 'Western']", "['Comedy', 'Drama',  
"['Western']"), class = "factor"), rating = c(5.3, 4.5, 7.8, 
 4.8, 7.1, 7.6)), row.names = c(NA, 6L), class = "data.frame")

内容的提问来源于stack exchange，提问作者RNewbie