ntjohnson1 opened a new issue, #1234:
URL: https://github.com/apache/datafusion-python/issues/1234
**Describe the bug**
with_column typically add a new column with the provided name. However, when
using lag we get two new columns, with the provided name and automatically
generate one.
**To Reproduce**
```python
import datafusion as dfn
from datafusion import col, lit, functions as F
import pyarrow as pa
def datafusion_example() -> None:
table = pa.table({"a": [1.0, 2.0, 3.0]})
ctx = dfn.SessionContext()
df = ctx.from_arrow(table)
print(
df.with_column(
"previous_a",
F.lag(
col("a"),
default_value=None,
),
)
)
print(df.with_column("something_else", col("a") + lit(1.0)))
if __name__ == "__main__":
datafusion_example()
```
Output
```console
DataFrame()
+-----+-----------------------------------------------------------------------------------------------------------------+------------+
| a | lag(ced8c2b3710c14382bd5eb58d49ffbd53.a,Int64(1),NULL) ROWS BETWEEN
UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING | previous_a |
+-----+-----------------------------------------------------------------------------------------------------------------+------------+
| 1.0 |
| |
| 2.0 | 1.0
| 1.0 |
| 3.0 | 2.0
| 2.0 |
+-----+-----------------------------------------------------------------------------------------------------------------+------------+
DataFrame()
+-----+----------------+
| a | something_else |
+-----+----------------+
| 1.0 | 2.0 |
| 2.0 | 3.0 |
| 3.0 | 4.0 |
+-----+----------------+
```
**Expected behavior**
```console
DataFrame()
+-----+------------+
| a | previous_a |
+-----+------------+
| 1.0 | |
| 2.0 | 1.0 |
| 3.0 | 2.0 |
+-----+------------+
DataFrame()
+-----+----------------+
| a | something_else |
+-----+----------------+
| 1.0 | 2.0 |
| 2.0 | 3.0 |
| 3.0 | 4.0 |
+-----+----------------+
```
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