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fix(memtable): ensure that constructing an empty memtable from a dataframe works #10945

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merged 2 commits into from
Mar 6, 2025
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fix(memtable): ensure that constructing an empty memtable from a dataframe works #10945

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509b6c0
test(memtable): add test for empty memtable
cpcloud Mar 6, 2025
22826a6
fix(memtable): ensure that empty memtables can be converted to pyarrow
cpcloud Mar 6, 2025
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15 changes: 15 additions & 0 deletions ibis/backends/tests/test_generic.py
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,7 @@
np = pytest.importorskip("numpy")
pd = pytest.importorskip("pandas")
tm = pytest.importorskip("pandas.testing")
pa = pytest.importorskip("pyarrow")

NULL_BACKEND_TYPES = {
"bigquery": "NULL",
Expand Down Expand Up @@ -2516,3 +2517,17 @@ def test_table_describe_with_multiple_decimal_columns(con):
expr = t.describe()
result = con.to_pyarrow(expr)
assert len(result) == 2


@pytest.mark.parametrize(
"input",
[[], pa.table([[]], pa.schema({"x": pa.int64()}))],
ids=["list", "pyarrow-table"],
)
@pytest.mark.notyet(["druid"], raises=PyDruidProgrammingError)
@pytest.mark.notyet(
["flink"], raises=ValueError, reason="flink doesn't support empty tables"
)
def test_empty_memtable(con, input):
t = ibis.memtable(input, schema={"x": "int64"})
assert not len(con.to_pyarrow(t))
13 changes: 11 additions & 2 deletions ibis/expr/api.py
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Original file line number Diff line number Diff line change
Expand Up @@ -429,15 +429,24 @@ def _memtable(
schema: SchemaLike | None = None,
name: str | None = None,
) -> Table:
import ibis

if hasattr(data, "__arrow_c_stream__"):
# Support objects exposing arrow's PyCapsule interface
import pyarrow as pa

data = pa.table(data)
data = pa.table(
data,
schema=ibis.schema(schema).to_pyarrow() if schema is not None else None,
)
else:
import pandas as pd

data = pd.DataFrame(data, columns=columns)
data = pd.DataFrame(
data,
columns=columns
or (ibis.schema(schema).names if schema is not None else None),
)
return _memtable(data, columns=columns, schema=schema, name=name)


Expand Down