alamb commented on code in PR #10260:
URL: https://github.com/apache/datafusion/pull/10260#discussion_r1581819093
##########
datafusion/expr/src/expr_fn.rs:
##########
@@ -215,6 +215,18 @@ pub fn count(expr: Expr) -> Expr {
))
}
+/// Create an expression to represent the count_null() aggregate function
Review Comment:
I think this function is creating a function like `COUNT(IS NULL x)` rather
than a `count_null` function
##########
datafusion/core/tests/dataframe/describe.rs:
##########
@@ -39,7 +39,7 @@ async fn describe() -> Result<()> {
"| describe | id | bool_col | tinyint_col |
smallint_col | int_col | bigint_col | float_col
| double_col | date_string_col | string_col | timestamp_col
| year | month |",
"+------------+-------------------+----------+--------------------+--------------------+--------------------+--------------------+--------------------+--------------------+-----------------+------------+-------------------------+--------------------+-------------------+",
"| count | 7300.0 | 7300 | 7300.0 |
7300.0 | 7300.0 | 7300.0 | 7300.0
| 7300.0 | 7300 | 7300 | 7300
| 7300.0 | 7300.0 |",
- "| null_count | 7300.0 | 7300 | 7300.0 |
7300.0 | 7300.0 | 7300.0 | 7300.0
| 7300.0 | 7300 | 7300 | 7300
| 7300.0 | 7300.0 |",
+ "| null_count | 0.0 | 0 | 0.0 |
0.0 | 0.0 | 0.0 | 0.0
| 0.0 | 0 | 0 | 0
| 0.0 | 0.0 |",
Review Comment:
that certainly looks better
##########
datafusion/core/src/dataframe/mod.rs:
##########
@@ -534,7 +534,7 @@ impl DataFrame {
vec![],
original_schema_fields
.clone()
- .map(|f| count(is_null(col(f.name()))).alias(f.name()))
+ .map(|f| count_null(col(f.name())).alias(f.name()))
Review Comment:
Instead of a `count_null()` new function, what do you think about using the
existing
[`count`](https://docs.rs/datafusion/latest/datafusion/logical_expr/fn.count.html)
function?
Something like `count(expr.is_null())`
```suggestion
.map(|f| count(col(f.name()).is_null()).alias(f.name())))
```
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