Modify doc for nanvl. (#7311)

Author: sarutak

datafusion/physical-expr/src/math_expressions.rs

@@ -1057,9 +1057,9 @@ mod tests {
             Arc::new(Float64Array::from(vec![5.0, 6.0, f64::NAN, f64::NAN])), // x
         ];
 
-        let result = nanvl(&args).expect("failed to initialize function atan2");
+        let result = nanvl(&args).expect("failed to initialize function nanvl");
         let floats =
-            as_float64_array(&result).expect("failed to initialize function atan2");
+            as_float64_array(&result).expect("failed to initialize function nanvl");
 
         assert_eq!(floats.len(), 4);
         assert_eq!(floats.value(0), 1.0);
@@ -1075,9 +1075,9 @@ mod tests {
             Arc::new(Float32Array::from(vec![5.0, 6.0, f32::NAN, f32::NAN])), // x
         ];
 
-        let result = nanvl(&args).expect("failed to initialize function atan2");
+        let result = nanvl(&args).expect("failed to initialize function nanvl");
         let floats =
-            as_float32_array(&result).expect("failed to initialize function atan2");
+            as_float32_array(&result).expect("failed to initialize function nanvl");
 
         assert_eq!(floats.len(), 4);
         assert_eq!(floats.value(0), 1.0);

docs/source/user-guide/expressions.md

@@ -101,6 +101,7 @@ expressions such as `col("a") + col("b")` to be used.
 | log(base, x)          | logarithm of x for a particular base              |
 | log10(x)              | base 10 logarithm                                 |
 | log2(x)               | base 2 logarithm                                  |
+| nanvl(x, y)           | returns x if x is not NaN otherwise returns y     |
 | pi()                  | approximate value of π                            |
 | power(base, exponent) | base raised to the power of exponent              |
 | radians(x)            | converts degrees to radians                       |