Added warning when adding a column to a table with different length (#58)

* test for dealing with the warning being thrown on empty tables
* added to the add_column test to check for the warning to be raised

Author: MoritzNeuberger

src/lgdo/types/table.py

@@ -78,7 +78,7 @@ def __init__(
 
         # if no col_dict, just set the size (default to 1024)
         else:
-            self.size = size if size is not None else 1024
+            self.size = size if size is not None else None
 
         # always start at loc=0
         self.loc = 0
@@ -137,8 +137,19 @@ def add_field(self, name: str, obj: LGDO, use_obj_size: bool = False) -> None:
 
         super().add_field(name, obj)
 
+        if self.size is None:
+            self.size = len(obj)
+
         # check / update sizes
         if self.size != len(obj):
+            warn(
+                f"warning: you are trying to add {name} with length {len(obj)} to a table with size {self.size} and data might be lost. \n"
+                f"With 'use_obj_size' set to:\n"
+                f"  - True, the table will be resized to length {len(obj)} by padding/clipping its columns.\n"
+                f"  - False (default), object {name} will be padded/clipped to length {self.size}.",
+                UserWarning,
+                stacklevel=2,
+            )
             new_size = len(obj) if use_obj_size else self.size
             self.resize(new_size=new_size)
 

tests/types/test_table.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import warnings
+
 import awkward as ak
 import numpy as np
 import pandas as pd
@@ -11,7 +13,7 @@
 
 def test_init():
     tbl = Table()
-    assert tbl.size == 1024
+    assert not tbl.size
     assert tbl.loc == 0
 
     tbl = Table(size=10)
@@ -68,6 +70,11 @@ def test_add_column():
     tbl = Table()
     tbl.add_column("a", lgdo.Array(np.array([1, 2, 3])), use_obj_size=True)
     assert tbl.size == 3
+    with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("always")
+        tbl.add_column("b", lgdo.Array(np.array([1, 2, 3, 4])))
+        assert len(w) == 1
+        assert issubclass(w[-1].category, UserWarning)
 
 
 def test_join():
@@ -88,7 +95,7 @@ def test_join():
 
 
 def test_view_as():
-    tbl = Table(4)
+    tbl = Table(3)
     tbl.add_column("a", lgdo.Array(np.array([1, 2, 3]), attrs={"units": "m"}))
     tbl.add_column("b", lgdo.Array(np.array([[0, 1, 2], [3, 4, 5], [6, 7, 8]])))
     tbl.add_column(
@@ -102,8 +109,8 @@ def test_view_as():
         "d",
         lgdo.Table(
             col_dict={
-                "a": lgdo.Array(np.array([2, 4, 6, 8]), attrs={"units": "m"}),
-                "b": lgdo.Array(np.array([[1, 1], [2, 4], [3, 9], [4, 16]])),
+                "a": lgdo.Array(np.array([2, 4, 6]), attrs={"units": "m"}),
+                "b": lgdo.Array(np.array([[1, 1], [2, 4], [3, 9]])),
             }
         ),
     )