Return File Path after Writing in fwrite

NEWS.md

@@ -44,6 +44,8 @@
 
 14. `fread` loads `.bgz` files directly, [#5461](https://github.com/Rdatatable/data.table/issues/5461). Thanks to @TMRHarrison for the request with proposed fix, and Benjamin Schwendinger for the PR.
 
+15. `fwrite` now returns the file path after writing data, [#5706](https://github.com/Rdatatable/data.table/issues/5706). This enhancement allows users to easily capture and utilize the file path for subsequent operations.Thanks to @Nj221102 for the PR.
+
 ## BUG FIXES
 
 1. `unique()` returns a copy the case when `nrows(x) <= 1` instead of a mutable alias, [#5932](https://github.com/Rdatatable/data.table/pull/5932). This is consistent with existing `unique()` behavior when the input has no duplicates but more than one row. Thanks to @brookslogan for the report and @dshemetov for the fix.

R/fwrite.R

@@ -84,11 +84,11 @@ fwrite = function(x, file="", append=FALSE, quote="auto",
     if (file.exists(file)) {
       suggested <- if (append) "" else gettextf("\nIf you intended to overwrite the file at %s with an empty one, please use file.remove first.", file)
       warningf("Input has no columns; doing nothing.%s", suggested)
-      return(invisible())
+      return(invisible(file))
     } else {
       warningf("Input has no columns; creating an empty file at '%s' and exiting.", file)
       file.create(file)
-      return(invisible())
+      return(invisible(file))
     }
   }
   yaml = if (!yaml) "" else {
@@ -118,7 +118,7 @@ fwrite = function(x, file="", append=FALSE, quote="auto",
   .Call(CfwriteR, x, file, sep, sep2, eol, na, dec, quote, qmethod=="escape", append,
         row.names, col.names, logical01, scipen, dateTimeAs, buffMB, nThread,
         showProgress, is_gzip, bom, yaml, verbose, encoding)
-  invisible()
+  invisible(file)
 }
 
 haszlib = function() .Call(Cdt_has_zlib)

inst/tests/tests.Rraw

@@ -9977,7 +9977,7 @@ test(1658.31, fwrite(ok_dt, qmethod=c("double", "double")), error="length(qmetho
 test(1658.32, fwrite(ok_dt, col.names="foobar"), error="isTRUEorFALSE(col.names)")
 
 # null data table (no columns)
-test(1658.33, fwrite(data.table(NULL)), NULL, warning="Nothing to write")
+test(1658.33, fwrite(data.table(NULL)), "", warning="Nothing to write")
 
 test(1658.34, fwrite(data.table(id=c("A","B","C"), v=c(1.1,0.0,9.9))), output="id,v\nA,1.1\nB,0\nC,9.9")
 
@@ -10009,9 +10009,9 @@ if (!haszlib()) {
 } else {
   test(1658.41, fwrite(data.table(a=c(1:3), b=c(1:3)), compress="gzip"), output='a,b\n1,1\n2,2\n3,3')  # compress ignored on console
   DT = data.table(a=rep(1:2,each=100), b=rep(1:4,each=25))
-  test(1658.421, fwrite(DT, file=f1<-tempfile(fileext=".gz"), verbose=TRUE), NULL,
+  test(1658.421, filepath <- fwrite(DT, file=f1<-tempfile(fileext=".gz"), verbose=TRUE), filepath,
                  output="args.nrow=200 args.ncol=2.*maxLineLen=5[12].*Writing 200 rows in 1 batches of 200 rows.*nth=1")  # [12] for Windows where eolLen==2
-  test(1658.422, fwrite(DT, file=f2<-tempfile()), NULL)
+  test(1658.422, filepath <- fwrite(DT, file=f2<-tempfile()), filepath)
   test(1658.423, file.info(f1)$size < file.info(f2)$size)  # 74 < 804  (file.size() isn't available in R 3.1.0)
   if (test_R.utils) test(1658.43, fread(f1), DT)  # use fread to decompress gz (works cross-platform)
   fwrite(DT, file=f3<-tempfile(), compress="gzip")   # compress to filename not ending .gz
@@ -10046,7 +10046,7 @@ unlink(c(f1, f2))
 # compression error -5 due to only 3 bytes (bom) in first block; #3599
 if (haszlib()) {
   DT = data.table(l=letters, n=1:26)
-  test(1658.53, fwrite(DT, file=f<-tempfile(fileext=".gz"), bom=TRUE, col.names=FALSE), NULL)
+  test(1658.53, filepath <- fwrite(DT, file=f<-tempfile(fileext=".gz"), bom=TRUE, col.names=FALSE), filepath)
   if (test_R.utils) test(1658.54, fread(f), setnames(DT,c("V1","V2")))
   unlink(f)
 }
@@ -10059,7 +10059,7 @@ test(1658.56, fwrite(data.table(exp(1) - pi*1i)), output='2.718[0-9]*-3.141[0-9]
 DT = data.table(a=1:3, b=list(1:4, c(3.14, 100e10), c(3i,4i,5i)))
 test(1658.57, fwrite(DT), output='0+3i|0+4i|0+5i')
 DT[ , b := c(1i, -1-1i, NA_complex_)]
-test(1658.58, fwrite(DT), output='a,b\n1,0\\+1i\n2,-1-1i\n3,$')
+test(1658.58, fwrite(DT), output='a,b\n1,0+1i\n2,-1-1i\n3,\n[1] ""')
 
 # more coverage
 test(1658.59, fwrite(data.table(a=list('a')), verbose=TRUE),
@@ -10809,7 +10809,7 @@ if (test_bit64) {
   test(1731.1, class(DT[[1L]]), "integer64")
   test(1731.2, fwrite(DT,na="__NA__"), output=ans)
   f = tempfile()
-  test(1731.3, fwrite(DT, f, na="__NA__"), NULL)
+  test(1731.3, filepath <- fwrite(DT, f, na="__NA__"), filepath)
   test(1731.4, readLines(f), ans)
   unlink(f)
   ans[1] = "V1"  # the field is unquoted under `quote=FALSE`
@@ -10910,7 +10910,7 @@ test(1736.09, capture.output(fwrite(DT)), c("A,B", "foo,1|2|3", "\"ba|r\",1|2|3|
 test(1736.10, capture.output(fwrite(DT,quote=TRUE)), c("\"A\",\"B\"", "\"foo\",1|2|3", "\"ba|r\",1|2|3|4", "\"baz\",\"fo|o\"|\"ba,r\"|\"baz\""))
 
 # any list of same length vector input
-test(1737.1, fwrite(list()), NULL, warning="fwrite was passed an empty list of no columns")
+test(1737.1, fwrite(list()), "", warning="fwrite was passed an empty list of no columns")
 test(1737.2, fwrite(list(1.2)), output="1.2")
 test(1737.3, fwrite(list(1.2,B="foo")), output=",B\n1.2,foo")
 test(1737.4, fwrite(list("A,Name"=1.2,B="fo,o")), output="\"A,Name\",B\n1.2,\"fo,o\"")
@@ -13089,11 +13089,11 @@ unlink(f)
 #fwrite creates a file or does nothing, as appropriate, also #2898
 DT = data.table(NULL)
 f = tempfile()
-test(1922.7, fwrite(DT, f), NULL, warning = 'no columns; creating an empty file')
+test(1922.7, filepath <- fwrite(DT, f), filepath, warning = 'no columns; creating an empty file')
 ## above test created a file; now test behavior when file exists
-test(1922.8, fwrite(DT, f), NULL, warning = 'no columns; doing nothing.*file.remove')
+test(1922.8, filepath <- fwrite(DT, f), filepath, warning = 'no columns; doing nothing.*file.remove')
 ## slightly different behavior if append = TRUE
-test(1922.9, fwrite(DT, f, append = TRUE), NULL, warning = 'doing nothing.$')
+test(1922.9, filepath <- fwrite(DT, f, append = TRUE), filepath, warning = 'doing nothing.$')
 
 # create index even if key present by setting attribute, #2883
 DT = data.table(1:5, 1:5)
@@ -13141,8 +13141,8 @@ test(1937.1, DT[A %between% c(B,B+1)], error='RHS has length().*Perhaps you mean
 test(1937.2, DT[A %between% B],        error='length 2. The first')
 
 # that fwrite'ing a list to a file works (it broke in dev 1.11.5 and was caught before release), PR#3017
-test(1938.1, fwrite(list(1:3)), NULL, output="1\n2\n3")    # never broke
-test(1938.2, fwrite(list(1:3), file=f<-tempfile()), NULL)  # just adding file= was what broke in dev just when x is list and not data.table|frame
+test(1938.1, fwrite(list(1:3)), "", output="1\n2\n3")    # never broke
+test(1938.2, filepath <- fwrite(list(1:3), file=f<-tempfile()), filepath)  # just adding file= was what broke in dev just when x is list and not data.table|frame
 test(1939.3, readLines(f), as.character(1:3))
 unlink(f)
 
@@ -13775,9 +13775,9 @@ if (.Platform$OS.type=="windows") {
   test(1966.4, list.files(path = pth, pattern = "\\.csv$"), f)
   unlink(c(fp, file.path(pth, "\u00c3\u00b6.csv")))
   p = file.path(pth, "\u00fc"); dir.create(p); f = tempfile(tmpdir = p)
-  test(1966.5, fwrite(DT, enc2native(f)), NULL)
+  test(1966.5, filepath <- fwrite(DT, enc2native(f)), filepath)
   unlink(f)
-  test(1966.6, fwrite(DT, enc2utf8(f)), NULL)
+  test(1966.6, filepath <- fwrite(DT, enc2utf8(f)), filepath)
   unlink(p, recursive = TRUE)
 }