Add isnan and iszero (#495)

* Add `isnan` and `iszero`

* Add test for `log`

* Add missing newline!

Co-authored-by: Liang-Chi Hsieh <viirya@gmail.com>

* Fix linting

---------

Co-authored-by: Liang-Chi Hsieh <viirya@gmail.com>

datafusion/tests/test_functions.py

@@ -131,6 +131,9 @@ def test_math_functions():
         f.sinh(col_v),
         f.tanh(col_v),
         f.factorial(literal(6)),
+        f.isnan(col_nav),
+        f.iszero(col_nav),
+        f.log(literal(3), col_v + literal(pa.scalar(1))),
     )
     batches = df.collect()
     assert len(batches) == 1
@@ -185,6 +188,13 @@ def test_math_functions():
     np.testing.assert_array_almost_equal(result.column(32), np.sinh(values))
     np.testing.assert_array_almost_equal(result.column(33), np.tanh(values))
     np.testing.assert_array_almost_equal(result.column(34), math.factorial(6))
+    np.testing.assert_array_almost_equal(
+        result.column(35), np.isnan(na_values)
+    )
+    np.testing.assert_array_almost_equal(result.column(36), na_values == 0)
+    np.testing.assert_array_almost_equal(
+        result.column(37), np.emath.logn(3, values + 1.0)
+    )
 
 
 def test_string_functions(df):

src/functions.rs

@@ -230,6 +230,8 @@ scalar_function!(factorial, Factorial);
 scalar_function!(floor, Floor);
 scalar_function!(gcd, Gcd);
 scalar_function!(initcap, InitCap, "Converts the first letter of each word to upper case and the rest to lower case. Words are sequences of alphanumeric characters separated by non-alphanumeric characters.");
+scalar_function!(isnan, Isnan);
+scalar_function!(iszero, Iszero);
 scalar_function!(lcm, Lcm);
 scalar_function!(left, Left, "Returns first n characters in the string, or when n is negative, returns all but last |n| characters.");
 scalar_function!(ln, Ln);
@@ -414,6 +416,8 @@ pub(crate) fn init_module(m: &PyModule) -> PyResult<()> {
     m.add_wrapped(wrap_pyfunction!(grouping))?;
     m.add_wrapped(wrap_pyfunction!(in_list))?;
     m.add_wrapped(wrap_pyfunction!(initcap))?;
+    m.add_wrapped(wrap_pyfunction!(isnan))?;
+    m.add_wrapped(wrap_pyfunction!(iszero))?;
     m.add_wrapped(wrap_pyfunction!(lcm))?;
     m.add_wrapped(wrap_pyfunction!(left))?;
     m.add_wrapped(wrap_pyfunction!(length))?;