Add isnan scalar function

datafusion/tests/test_functions.py

@@ -131,6 +131,7 @@ def test_math_functions():
         f.sinh(col_v),
         f.tanh(col_v),
         f.factorial(literal(6)),
+        f.isnan(col_nav),
     )
     batches = df.collect()
     assert len(batches) == 1
@@ -185,6 +186,7 @@ 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))
 
 
 def test_string_functions(df):

src/functions.rs

@@ -230,6 +230,7 @@ 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, "Returns true if a given number is +NaN or -NaN otherwise returns false.");
 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);
@@ -247,7 +248,7 @@ scalar_function!(
 scalar_function!(
     nanvl,
     Nanvl,
-    "Computes the MD5 hash of the argument, with the result written in hexadecimal."
+    "Returns x if x is not NaN otherwise returns y."
 );
 scalar_function!(octet_length, OctetLength, "Returns number of bytes in the string. Since this version of the function accepts type character directly, it will not strip trailing spaces.");
 scalar_function!(pi, Pi);