Implement Mean and Sum for Boolean Columns and Implement approx_nuniq…

…ue and summary in BQ

Closes #1516

Author: Scott Lustig <scott.lustig@twosigma.com>

Closes #1517 from missing-semicolon/reduction and squashes the following commits:

80a1672 [Scott Lustig] Implement approx_nunique for BigQuery
c40b03a [Scott Lustig] Implement test for summary and approx_nunique
65680ff [Scott Lustig] Handle where argument when casting boolean columns
3610e67 [Scott Lustig] Add tests with where statement
96b2548 [Scott Lustig] Rewrite Mean and Sum for booleans
599b549 [Scott Lustig] Implement tests

ibis/bigquery/compiler.py

@@ -23,7 +23,7 @@
 import ibis.expr.lineage as lin
 
 from ibis.impala.compiler import (
-    ImpalaSelect, unary, fixed_arity, ImpalaTableSetFormatter
+    ImpalaSelect, unary, fixed_arity, ImpalaTableSetFormatter, _reduction
 )
 from ibis.impala import compiler as impala_compiler
 
@@ -397,6 +397,7 @@ def _formatter(translator, expr):
     ops.ArrayIndex: _array_index,
     ops.ArrayLength: unary('ARRAY_LENGTH'),
 
+    ops.HLLCardinality: _reduction('APPROX_COUNT_DISTINCT'),
     ops.Log: _log,
     ops.Sign: unary('SIGN'),
     ops.Modulus: fixed_arity('MOD', 2),
@@ -558,6 +559,26 @@ def log2(expr):
     return arg.log(2)
 
 
+@rewrites(ops.Sum)
+def bq_sum(expr):
+    arg = expr.op().args[0]
+    where = expr.op().args[1]
+    if isinstance(arg, ir.BooleanColumn):
+        return arg.cast('int64').sum(where=where)
+    else:
+        return expr
+
+
+@rewrites(ops.Mean)
+def bq_mean(expr):
+    arg = expr.op().args[0]
+    where = expr.op().args[1]
+    if isinstance(arg, ir.BooleanColumn):
+        return arg.cast('int64').mean(where=where)
+    else:
+        return expr
+
+
 UNIT_FUNCS = {
     's': 'SECONDS',
     'ms': 'MILLIS',

ibis/bigquery/tests/test_client.py

@@ -604,3 +604,19 @@ def test_day_of_week(client, case, dtype):
     expr_name = date_var.day_of_week.full_name()
     result = client.execute(expr_name)
     assert result == 'Sunday'
+
+
+def test_boolean_reducers(alltypes):
+    b = alltypes.bool_col
+    bool_avg = b.mean().execute()
+    assert type(bool_avg) == np.float64
+
+    bool_sum = b.sum().execute()
+    assert type(bool_sum) == np.int64
+
+
+def test_column_summary(alltypes):
+    b = alltypes.bool_col.summary()
+    result = b.execute()
+    assert result.shape == (1, 7)
+    assert len(result) == 1

ibis/bigquery/tests/test_compiler.py

@@ -384,3 +384,57 @@ def test_projection_fusion_only_peeks_at_immediate_parent():
 FROM t3
   CROSS JOIN t3 t4"""
     assert result == expected
+
+
+def test_bool_reducers(alltypes):
+    b = alltypes.bool_col
+    expr = b.mean()
+    result = expr.compile()
+    expected = """\
+SELECT avg(CAST(`bool_col` AS INT64)) AS `mean`
+FROM `ibis-gbq.testing.functional_alltypes`"""
+    assert result == expected
+
+    expr2 = b.sum()
+    result = expr2.compile()
+    expected = """\
+SELECT sum(CAST(`bool_col` AS INT64)) AS `sum`
+FROM `ibis-gbq.testing.functional_alltypes`"""
+    assert result == expected
+
+
+def test_bool_reducers_where(alltypes):
+    b = alltypes.bool_col
+    m = alltypes.month
+    expr = b.mean(where=m > 6)
+    result = expr.compile()
+    expected = """\
+SELECT avg(CASE WHEN `month` > 6 THEN CAST(`bool_col` AS INT64) ELSE NULL END) AS `mean`
+FROM `ibis-gbq.testing.functional_alltypes`"""  # noqa: E501
+    assert result == expected
+
+    expr2 = b.sum(where=((m > 6) & (m < 10)))
+    result = expr2.compile()
+    expected = """\
+SELECT sum(CASE WHEN (`month` > 6) AND (`month` < 10) THEN CAST(`bool_col` AS INT64) ELSE NULL END) AS `sum`
+FROM `ibis-gbq.testing.functional_alltypes`"""  # noqa: E501
+    assert result == expected
+
+
+def test_approx_nunique(alltypes):
+    d = alltypes.double_col
+    expr = d.approx_nunique()
+    result = expr.compile()
+    expected = """\
+SELECT APPROX_COUNT_DISTINCT(`double_col`) AS `approx_nunique`
+FROM `ibis-gbq.testing.functional_alltypes`"""
+    assert result == expected
+
+    b = alltypes.bool_col
+    m = alltypes.month
+    expr2 = b.approx_nunique(where=m > 6)
+    result = expr2.compile()
+    expected = """\
+SELECT APPROX_COUNT_DISTINCT(CASE WHEN `month` > 6 THEN `bool_col` ELSE NULL END) AS `approx_nunique`
+FROM `ibis-gbq.testing.functional_alltypes`"""  # noqa: E501
+    assert result == expected