fwrite coerces input to data.table when given a matrix (#3125)

NEWS.md

@@ -12,6 +12,8 @@
 
 4. `NA` in `between`'s `lower` and `upper` are now taken as missing bounds and return `TRUE` rather than than `NA`. This is now documented.
 
+5. `fwrite()` now accepts `matrix`, (#2613)[https://github.com/Rdatatable/data.table/issues/2613]. Thanks to Michael Chirico for the suggestion and Felipe Parages for implementing. For now matrix input is converted to data.table (which can be costly) before writing. 
+
 #### BUG FIXES
 
 1. Providing an `i` subset expression when attempting to delete a column correctly failed with helpful error, but when the column was missing too created a new column full of `NULL` values, [#3089](https://github.com/Rdatatable/data.table/issues/3089). Thanks to Michael Chirico for reporting.

R/fwrite.R

@@ -26,6 +26,10 @@ fwrite <- function(x, file="", append=FALSE, quote="auto",
   nThread = as.integer(nThread)
   # write.csv default is 'double' so fwrite follows suit. write.table's default is 'escape'
   # validate arguments
+  if (is.matrix(x)) { # coerce to data.table if input object is matrix
+    message("x being coerced from class: matrix to data.table")
+    x <- as.data.table(x)
+  }
   stopifnot(is.list(x),
     identical(quote,"auto") || identical(quote,FALSE) || identical(quote,TRUE),
     is.character(sep) && length(sep)==1L && nchar(sep) == 1L,

inst/tests/tests.Rraw

@@ -9213,6 +9213,12 @@ test(1658.32, fwrite(data.table(D = as.POSIXct(seq.Date(as.Date("2038-01-19"), a
 
 options(oldverbose)
 
+# input is of class matrix
+test(1658.33, fwrite(matrix("foo"), quote=TRUE), output='"V1"\n"foo"', message = "x being coerced from class: matrix to data.table")
+test(1658.34, fwrite(matrix(1:4, nrow=2, ncol=2), quote = TRUE), output = '"V1","V2"\n1,3\n2,4', message = "x being coerced from class: matrix to data.table")
+test(1658.35, fwrite(matrix(1:3, nrow=3, ncol=1), quote = TRUE), output = '"V1"\n1\n2\n3', message = "x being coerced from class: matrix to data.table")
+test(1658.36, fwrite(matrix(1:4, nrow=2, ncol=2, dimnames = list(c("ra","rb"),c("ca","cb"))), quote = TRUE), output = '"ca","cb"\n1,3\n2,4', message = "x being coerced from class: matrix to data.table")
+
 ## End fwrite tests
 
 # tests for #679, inrange(), FR #707

man/fwrite.Rd

@@ -20,7 +20,7 @@ fwrite(x, file = "", append = FALSE, quote = "auto",
   verbose = getOption("datatable.verbose", FALSE))
 }
 \arguments{
-  \item{x}{Any \code{list} of same length vectors; e.g. \code{data.frame} and \code{data.table}.}
+  \item{x}{Any \code{list} of same length vectors; e.g. \code{data.frame} and \code{data.table}. If \code{matrix}, it gets internally coerced to \code{data.table} preserving col names but not row names}
   \item{file}{Output file name. \code{""} indicates output to the console. }
   \item{append}{If \code{TRUE}, the file is opened in append mode and column names (header row) are not written.}
   \item{quote}{When \code{"auto"}, character fields, factor fields and column names will only be surrounded by double quotes when they need to be; i.e., when the field contains the separator \code{sep}, a line ending \code{\\n}, the double quote itself or (when \code{list} columns are present) \code{sep2[2]} (see \code{sep2} below). If \code{FALSE} the fields are not wrapped with quotes even if this would break the CSV due to the contents of the field. If \code{TRUE} double quotes are always included other than around numeric fields, as \code{write.csv}.}