fix: sub-day precision Date should be floored when treated as integer

R/write-parquet.R

@@ -162,10 +162,9 @@ prepare_write_df <- function(x) {
   }
 
   # Date must be integer
-  dates <- which(vapply(x, "inherits", "Date", FUN.VALUE = logical(1)))
-  for (idx in dates) {
-    # this keeps the class
-    mode(x[[idx]]) <- "integer"
+  double_dates <- which(vapply(x, function(x) inherits(x, "Date") && is.double(x), FUN.VALUE = logical(1)))
+  for (idx in double_dates) {
+    x[[idx]] <- .Date(as.integer(floor(as.numeric(x[[idx]]))))
   }
 
   # Convert hms to double
@@ -405,4 +404,4 @@ append_parquet <- function(
   } else {
     res
   }
-}
+}

tests/testthat/test-write-parquet-2.R

@@ -186,3 +186,18 @@ test_that("zstd compression", {
   expect_equal(read_parquet_page(tmp, 4L)$codec, "ZSTD")
   expect_equal(read_parquet(tmp), d);
 })
+
+test_that("Conversion of sub-dates prior Posix origin is correct", {
+  data <- data.frame(
+    days = as.Date(c(-1.1, -0.1, 0, 0.1, 1.1), origin = "1970-01-01")
+  )
+
+  tmp <- tempfile(fileext = ".parquet")
+  on.exit(unlink(tmp), add = TRUE)
+
+  write_parquet(data, tmp)
+  expect_equal(
+    as.character(as.data.frame(read_parquet(tmp))$date),
+    as.character(data$date)
+  )
+})