[pack_dataset] don't sort before packing, only pack train (#5954)

examples/seq2seq/minify_dataset.py

@@ -0,0 +1,19 @@
+from pathlib import Path
+
+import fire
+
+
+def minify(src_dir: str, dest_dir: str, n: int):
+    """Write first n lines of each file f in src_dir to dest_dir/f """
+    src_dir = Path(src_dir)
+    dest_dir = Path(dest_dir)
+    dest_dir.mkdir(exist_ok=True)
+    for path in src_dir.iterdir():
+        new = [x.rstrip() for x in list(path.open().readlines())][:n]
+        dest_path = dest_dir.joinpath(path.name)
+        print(dest_path)
+        dest_path.open("w").write("\n".join(new))
+
+
+if __name__ == "__main__":
+    fire.Fire(minify)