How to extract text from a column using R - r

Question

How would I go about extracting, for each row (there are ~56,000 records in an Excel file) in a specific column, only part of a string? I need to keep all text to the left of the last '/' forward slash. The challenge is that not all cells have the same number of '/'. There is always a filename (*.wav) at the end of the last '/', but the number of characters in the filename is not always the same (sometimes 5 and sometimes 6).
Below are some examples of the strings in the cells:
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
The extracted text should be:
cloch
grand/Grand_bombarde/02-suchy_Grand_bombarde
grand/Grand_bombarde/02-suchy_Grand_bombarde
AB_AeolinaL
AB_AeolinaL
AB_violadamourL/rel99999
AB_violadamourL/rel99999
AB_violadamourR
AB_violadamourR
Can anyone recommend a strategy using R?

Answer 1

You can use the stringr package str_remove(string,pattern) function like:
str = "grand/Grand_bombarde/02-suchy_Grand_bombarde/038-D.wav"
str_remove(str,"/[0-9]+[-]*[A-Z]*[#]*[.][a-z]+")
Output:
> str_remove(str,"/[0-9]+[-]*[A-Z]*[#]*[.][a-z]+")
[1] "grand/Grand_bombarde/02-suchy_Grand_bombarde"
Then you can just iterate over all other strings:
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]+")
Output:
> 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

You have to substract strings using this method:
substr(strings,1,regexpr("\\/[^\\/]*$", strings)-1)
[1] "cloch"
[2] "grand/Grand_bombarde/02-suchy_Grand_bombarde"
[3] "grand/Grand_bombarde/02-suchy_Grand_bombarde"
[4] "AB_AeolinaL"
[5] "AB_AeolinaL"
[6] "AB_violadamourL/rel99999"
[7] "AB_violadamourL/rel99999"
[8] "AB_violadamourR"
[9] "AB_violadamourR"
Input
strings<-c("cloch/51.wav","grand/Grand_bombarde/02-suchy_Grand_bombarde/038-D.wav","grand/Grand_bombarde/02-suchy_Grand_bombarde/039-D#.wav","AB_AeolinaL/025-C#.wav","AB_AeolinaL/026-D.wav","AB_violadamourL/rel99999/091-G.wav","AB_violadamourL/rel99999/092-G#.wav","AB_violadamourR/024-C.wav","AB_violadamourR/025-C#.wav")
In which this regex regexpr("\\/[^\\/]*$", strings) gives you the position of the last "/"

Answer 3

Assuming that the strings you propose are in a column of a dataframe:
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"

Answer 4

You could use
dirname(strings)
If there is no /, this returns ., which you could remove afterwards if you like, e.g.:
res <- dirname(strings)
res[res=="."] <- ""
``

Answer 5

You could start the match with / followed by 1 or more times any char except a forward slash or a whitespace char using a negated character class [^\\s/]+
Then match .wav at the end of the string using $
Replace the match with an empty string using sub for example.
[^\\s/]+\\.wav$
See the regex matches | R demo
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")
sub("/[^\\s/]+\\.wav$", "", strings)
Output
[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"