BUG: Fixes pandas-dev#54617 Dataframe to html for empty array with complex dtypes (pandas-dev#54451)

* Fresh new feature

* Removed html file, put it in string in the test

* Html test against hash value

* Removing prints

* Keeping inline html instead of mdlib hex

* added an entry in the io section

* Update doc/source/whatsnew/v2.1.0.rst

Co-authored-by: Matthew Roeschke <[email protected]>

* Modifying rst file

* Sorted rst file after manual run of precommit on local

---------

Co-authored-by: Matthew Roeschke <[email protected]>

Author: soumya1729

doc/source/whatsnew/v2.1.0.rst

@@ -731,6 +731,7 @@ I/O
 - Bug in :func:`read_sql` when reading multiple timezone aware columns with the same column name (:issue:`44421`)
 - Bug in :func:`read_xml` stripping whitespace in string data (:issue:`53811`)
 - Bug in :meth:`DataFrame.to_html` where ``colspace`` was incorrectly applied in case of multi index columns (:issue:`53885`)
+- Bug in :meth:`DataFrame.to_html` where conversion for an empty :class:`DataFrame` with complex dtype raised a ``ValueError`` (:issue:`54167`)
 - Bug in :meth:`DataFrame.to_json` where :class:`DateTimeArray`/:class:`DateTimeIndex` with non nanosecond precision could not be serialized correctly (:issue:`53686`)
 - Bug when writing and reading empty Stata dta files where dtype information was lost (:issue:`46240`)
 - Bug where ``bz2`` was treated as a hard requirement (:issue:`53857`)

pandas/io/formats/format.py

@@ -1960,6 +1960,8 @@ def _trim_zeros_complex(str_complexes: np.ndarray, decimal: str = ".") -> list[s
     # in the array
     n = len(str_complexes)
     padded_parts = _trim_zeros_float(real_part + imag_part, decimal)
+    if len(padded_parts) == 0:
+        return []
     padded_length = max(len(part) for part in padded_parts) - 1
     padded = [
         real_pt  # real part, possibly NaN

pandas/tests/io/formats/test_to_html.py

@@ -959,3 +959,22 @@ def test_to_html_tuple_col_with_colspace():
         "</table>"
     )
     assert result == expected
+
+
+def test_to_html_empty_complex_array():
+    # GH#54167
+    df = DataFrame({"x": np.array([], dtype="complex")})
+    result = df.to_html(col_space=100)
+    expected = (
+        '<table border="1" class="dataframe">\n'
+        "  <thead>\n"
+        '    <tr style="text-align: right;">\n'
+        '      <th style="min-width: 100px;"></th>\n'
+        '      <th style="min-width: 100px;">x</th>\n'
+        "    </tr>\n"
+        "  </thead>\n"
+        "  <tbody>\n"
+        "  </tbody>\n"
+        "</table>"
+    )
+    assert result == expected