如何使用R从列中提取文本

Question

对于特定列中的每一行( Excel文件中有56,000条记录)，如何提取字符串的一部分？我需要将所有文本保持在最后的“/”斜杠的左边。挑战在于，并非所有的单元格都有相同数量的“/”。在最后一个'/‘结尾总是有一个文件名(*.wav)，但是文件名中的字符数并不总是相同的(有时是5个，有时是6个)。

下面是单元格中字符串的一些示例：

cloch/51.wav

grand/Grand_bombarde/02-suchy_Grand_bombarde/038-D.wav

grand/Grand_bombarde/02-suchy_Grand_bombarde/039-D#.wav

AB_AeolinaL/025-C#..wav

AB_AeolinaL/026-D.wav

AB_violadamourL/rel99999/091-G.wav

AB_violadamourL/rel99999/092-G#..wav

AB_violadamourR/024-C.wav

AB_violadamourR/025-C#..wav

摘录的案文应如下：

克洛奇

大/大轰炸/02-苏西_大轰炸

大/大轰炸/02-苏西_大轰炸

AB_AeolinaL

AB_AeolinaL

AB_violadamourL/rel99999

AB_violadamourL/rel99999

AB_violadamourR

AB_violadamourR

有人能推荐使用R的策略吗？

Answer 1

可以使用stringr包str_remove(string,pattern)函数，如下所示：

str = "grand/Grand_bombarde/02-suchy_Grand_bombarde/038-D.wav"
str_remove(str,"/[0-9]+[-]*[A-Z]*[#]*[.][a-z]+")

输出：

> str_remove(str,"/[0-9]+[-]*[A-Z]*[#]*[.][a-z]+")
[1] "grand/Grand_bombarde/02-suchy_Grand_bombarde"

然后，您只需遍历所有其他字符串：

strings <- c("cloch/51.wav",
             "grand/Grand_bombarde/02-suchy_Grand_bombarde/038-D.wav",
             "grand/Grand_bombarde/02-suchy_Grand_bombarde/039-D#.wav",
             "AB_AeolinaL/025-C#.wav",
             "AB_AeolinaL/026-D.wav",
             "AB_violadamourL/rel99999/091-G.wav",
             "AB_violadamourL/rel99999/092-G#.wav",
             "AB_violadamourR/024-C.wav",
             "AB_violadamourR/025-C#.wav")
str_remove(strings,"/[0-9]+[-]*[A-Z]*[#]*[.][a-z]+")

输出：

> str_remove(strings,"/[0-9]+[-]*[A-Z]*[#]*[.][a-z]+")
[1] "cloch"                                       
[2] "grand/Grand_bombarde/02-suchy_Grand_bombarde"
[3] "grand/Grand_bombarde/02-suchy_Grand_bombarde"
[4] "AB_AeolinaL"                                 
[5] "AB_AeolinaL"                                 
[6] "AB_violadamourL/rel99999"                    
[7] "AB_violadamourL/rel99999"                    
[8] "AB_violadamourR"                             
[9] "AB_violadamourR"  

Answer 2

必须使用此方法将字符串减为子字符串：

substr(strings,1,regexpr("\\/[^\\/]*$", strings)-1)
[1] "cloch"                                       
[2] "grand/Grand_bombarde/02-suchy_Grand_bombarde"
[3] "grand/Grand_bombarde/02-suchy_Grand_bombarde"
[4] "AB_AeolinaL"                                 
[5] "AB_AeolinaL"                                 
[6] "AB_violadamourL/rel99999"                    
[7] "AB_violadamourL/rel99999"                    
[8] "AB_violadamourR"                             
[9] "AB_violadamourR"

输入

strings<-c("cloch/51.wav","grand/Grand_bombarde/02-suchy_Grand_bombarde/038-D.wav","grand/Grand_bombarde/02-suchy_Grand_bombarde/039-D#.wav","AB_AeolinaL/025-C#.wav","AB_AeolinaL/026-D.wav","AB_violadamourL/rel99999/091-G.wav","AB_violadamourL/rel99999/092-G#.wav","AB_violadamourR/024-C.wav","AB_violadamourR/025-C#.wav")

其中正则表达式regexpr("\\/[^\\/]*$", strings)给出最后一个"/“的位置。

Answer 3

假设您提议的字符串位于dataframe的列中：

df <- data.frame(x = 1:5, y = c("cloch/51.wav", 
                                "grand/Grand_bombarde/02-suchy_Grand_bombarde/038-D.wav", 
                                "grand/Grand_bombarde/02-suchy_Grand_bombarde/039-D#.wav", 
                                "AB_AeolinaL/025-C#.wav", 
                                "AB_AeolinaL/026-D.wav"))

# I define a function that separates a string at each "/" 
# throws the last piece and reattaches the pieces

cut_str <- function(s) {
  st <- head((unlist(strsplit(s, "\\/"))), -1)
  r <- paste(st, collapse = "/")
  return(r)
}

# through the sapply function I get the desired result

new_strings <- as.vector(sapply(df$y, FUN = cut_str))
new_strings

[1] "cloch"                                       
[2] "grand/Grand_bombarde/02-suchy_Grand_bombarde"
[3] "grand/Grand_bombarde/02-suchy_Grand_bombarde"
[4] "AB_AeolinaL"                                 
[5] "AB_AeolinaL"