Using R, Retrieve files which filenames that contains certain strings - regex

Question

I have thousand of files from a certain directory:
filenames <- list.files("D:/MessData_Source", pattern="*.DAT", full.names=TRUE)
.....
.....
[9998] "D:/MessData_Source/908-A0F7__01310012567794F.DAT"
[9999] "D:/MessData_Source/908-A0F7__01310015662858F.DAT"
[10000] "D:/MessData_Source/908-A0F7__01310015662859F.DAT"
....
....
Out of those more than 1000 files, I need to extract out ONLY those files with filenames which contain certain strings.
e.g.
filename_extracted <- list()
for (i in 1:length(filenames))
{
# search for those filenames that contain the strings with PartNo and MoNo and store in results
filename_extracted[[i]] <- substr(filenames[i],31,43)
}
Above I am extracting the filenames string from number 31 to 43 and store it in filename_extracted which is something like this:
[[9993]]
[1] "1856955908850"
[[9994]]
[1] "1856955933372"
[[9995]]
[1] "1856955933372"
[[9996]]
[1] "1856955954613"
[[9997]]
[1] "1856955954613"
[[9998]]
[1] "1310012567794"
[[9999]]
[1] "1310015662858"
[[10000]]
[1] "1310015662859"
Next, I need to compare the filename_extracted to my required list, and copy those matched files to another directory.
required_list <- list()
df <-read.csv("PartNo_MoNo.csv") # full set
for (i in 1:length(df))
{
required_list[[i]] <- paste(df[i,1],df[i,2], sep="")
}
> required_list
[[1]]
[1] "1235235987252"
[[2]]
[1] "1897865985468"
If there are matches between required_list and filename_extracted, I want to copy the matched files to another directory, how do I do it?
thanks.

Answer 1

Here is the updated code, fully vectorized:
filename_extracted = substr(filenames, start=31, stop=43)
prefix = substr(filesnames, start=20, stop=30)
required_list = paste0(df[,1], df[,2])
common_suffix = intersect(filename_extracted, required_list)
common_prefix = prefix[filename_extracted %in% common]
storeDir = "D:/MessData_Source"
otherDir = "D:/OrderedData_Source"
if(length(common!=0))
{
commonFile = paste0(common_prefix, common_suffix, ".DAT")
sapply(commonFile, function(u){
file.copy(file.path(storeDir,u), file.path(otherDir, u))
})
}
Before executing this, make sure otherDir is created.

Answer 2

# Create data
library(stringr)
lapply(1:10, function(x){
write.csv(head(iris),file=paste0("908-A0F7__",x,".csv"))
write.csv(head(iris),file=paste0("notused__",x,".csv"))
})
# Only get files with correct pattern
pattern = "908-A0F7__(\\d+).csv"
files = data.frame(name=dir(pattern=pattern,full.names=TRUE))
files$num = as.integer(str_match(filenames$name,pattern)[,2])
required = c(1,3,5) # You can also read this in from your csv
myFiles = files[files$num %in% required,]
dir.create("copied")
file.copy(as.character(myFiles$name),file.path("copied",str_sub(myFiles$name,3)))