kosiew commented on code in PR #1041:
URL:
https://github.com/apache/datafusion-python/pull/1041#discussion_r1980965152
##########
src/dataframe.rs:
##########
@@ -90,59 +90,108 @@ impl PyDataFrame {
}
fn __repr__(&self, py: Python) -> PyDataFusionResult<String> {
- let df = self.df.as_ref().clone().limit(0, Some(10))?;
+ // Get 11 rows to check if there are more than 10
+ let df = self.df.as_ref().clone().limit(0, Some(11))?;
let batches = wait_for_future(py, df.collect())?;
- let batches_as_string = pretty::pretty_format_batches(&batches);
+ let num_rows = batches.iter().map(|batch|
batch.num_rows()).sum::<usize>();
+
+ // Flatten batches into a single batch for the first 10 rows
+ let mut all_rows = Vec::new();
+ let mut total_rows = 0;
+
+ for batch in &batches {
+ let num_rows_to_take = if total_rows + batch.num_rows() > 10 {
+ 10 - total_rows
+ } else {
+ batch.num_rows()
+ };
+
+ if num_rows_to_take > 0 {
+ let sliced_batch = batch.slice(0, num_rows_to_take);
+ all_rows.push(sliced_batch);
+ total_rows += num_rows_to_take;
+ }
+
+ if total_rows >= 10 {
+ break;
+ }
+ }
+
+ let batches_as_string = pretty::pretty_format_batches(&all_rows);
+
Review Comment:
> calling collect twice led to a severe performance degradation
I ran this test to compare the performance:
```python
import pyarrow as pa
from datafusion import (
SessionContext,
)
import time
def run_dataframe_repr_long() -> None:
ctx = SessionContext()
# Create a DataFrame with more than 10 rows
batch = pa.RecordBatch.from_arrays(
[
pa.array(list(range(15))),
pa.array([x * 2 for x in range(15)]),
pa.array([x * 3 for x in range(15)]),
],
names=["a", "b", "c"],
)
df = ctx.create_dataframe([[batch]])
output = repr(df)
def average_runtime(func, runs=100):
total_time = 0
for _ in range(runs):
start_time = time.time()
func()
end_time = time.time()
total_time += end_time - start_time
return total_time / runs
average_time = average_runtime(run_dataframe_repr_long)
print(f"Average runtime over {100} runs: {average_time:.6f} seconds")
```
and found no significant difference:
<img width="515" alt="image"
src="https://github.com/user-attachments/assets/e58bb136-2097-4b3e-8e4d-b1648cf29078";
/>
pr_1041 - is the branch with one `collect`
amended_pr_1041 - is the branch with two `collect`
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