How to check if filename ends with a certain string? (R)-CodePudding

I have the following code:

for (fileName in fileNames) {
    index <- "0"
      
      if (grepl("_01", fileName, fixed = TRUE)) {
        index <- "01"
      }
      
      if (grepl("_02", fileName, fixed = TRUE)) {
        index <- "02"
      }
}

and so on.

My filename is like "31231_sad_01.csv" or "31231_happy_01.csv".

All of my filenames are stored in a character vector fileNames. I loop through each file.

How can I find the past ending part of the filename aka 01 in this case or 02?

I tried using the code I mentioned and it always returns 1 for every value.

CodePudding user response：

Try the following:

#suppose you have your file names in a character vector

fnames <- c("31231_sad_01.csv", "31231_happy_02.csv") unlist(lapply(str_extract_all(fnames,"\\d "),'[',2))

It would return a vector

[1] "01" "02"

CodePudding user response：

An alternative way is to use sub to extract parts of the strings. Your examples show that the targeted index in each file name is always located after _ and before .csv. We can use this pattern in sub:

library(magrittr)

findex <- function(filename){ 
           filename %>% 
           sub(".csv.*" , "", .) %>%  #extract the part before ".csv"
           sub(".*_" , "", .)         # exctract the part after "_"
          }

This method can be used for various length of the index.

Test:

findex("31231_sad_01.csv")
#[1] "01"
findex("31231_happy_02.csv")
#[1] "02"
findex("31231_happy_213.csv")
#[1] "213"
findex("31231_happy_15213.csv")
#[1] "15213"

Then, you can use lapply or vapply to the vector that contains all the names:

names <- c("31231_happy_1032.csv", "31231_happy_02.csv", "31231_happy_213.csv", "31231_happy_15213.csv")
lapply(names, findex)
#[[1]]
#[1] "1032"

#[[2]]
#[1] "02"

#[[3]]
#[1] "213"

#[[4]]
#[1] "15213"

vapply(names, findex, character(1))
#31231_happy_1032.csv    31231_happy_02.csv   31231_happy_213.csv 
               "1032"                  "02"                 "213" 
#31231_happy_15213.csv 
              "15213"

In case you want to use only base R, this should work:

findex1 <- function(filename) sub(".*_" , "",  sub(".csv.*" , "", filename))

vapply(names, findex1, character(1))
# 31231_happy_1032.csv    31231_happy_02.csv   31231_happy_213.csv 
#               "1032"                  "02"                 "213" 
#31231_happy_15213.csv 
#              "15213"

CodePudding user response：

Vectorized alternatives exist, there is no need for a loop.

To check if the last numeric part of filename ends with a specific number, here 01, we can first extract the numeric part, then run endsWith.

string <- c("31231_sad_01.csv", "bla_215.csv", "test_05.csv")
endsWith(stringr::str_extract(string, "([^_])*(?=.csv)"), "01")

#> [1]  TRUE FALSE FALSE