Find second-from-last modified file in folder rather than final modified file in folder

user_17137505 0
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the below code finds the most recently modified file within a folder. Can anyone advise please how this can be amended to instead find the penultimate/second to last file that was modified? Can the which.max be amended to search for a -1 or is alternative code required?

#Open latest file
#get a vector of all filenames 
files <- list.files(path="MYFILEPATH",pattern="files.xls",full.names = TRUE,recursive = TRUE)

#get the directory names of these (for grouping)
dirs <- dirname(files)

#find the last file in each directory (i.e. latest modified time)
lastfiles <- tapply(files,dirs,function(v) v[which.max(file.mtime(v))])

File_List <- file.info(list.files("//MYFILEPATH", full.names = T))

Path_Of_Interest <- rownames(File_List)[which.max(File_List$mtime)]
r
2 Answers

Split the files by directory, then loop, order and get the 2nd from the last:

lapply(split(files, dirname(files)), function(i){
    i[ order(file.mtime(i)) ][ length(i) - 1 ]
  })
user_6800680

Something like this?
Instead of getting the entire file.info, the code below calls file.mtime.
Tested with files in a sub-directory of my home dir.

# my tmp dir
MYFILEPATH <- "~/tmp"

# get a vector of all filenames
files <- list.files(
  path=MYFILEPATH,
  pattern="\\.txt$",
  full.names = TRUE,
  recursive = TRUE
)

File_mtime <- file.mtime(files)
i <- order(File_mtime, decreasing = TRUE)
Second_Path <- if(length(i) > 1L) files[ i[2L] ] else files
Second_Path

The code above as a function.
The default is to return the last file changed. Argument default n = 1 must set to n = 2 for the function to return the before-last file changed.

nth_from_last_changed <- function(path = ".", pattern = NULL, n = 1L,
                                  full.names = TRUE, recursive = TRUE, ...){
  #get a vector of all filenames
  files <- list.files(
    path = path,
    pattern = pattern,
    full.names = full.names,
    recursive = recursive,
    ...
  )

  # get their last change time and order decreasing
  i <- order(file.mtime(files), decreasing = TRUE)
  if(length(i) > n - 1L) 
    files[ i[n] ] 
  else files[length(i)]
}

nth_from_last_changed("~/tmp", "\\.txt", n = 2)
user_82454060
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