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clarify semantics in order_by docstring #518

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Nov 3, 2024
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clarify semantics in order_by docstring #518

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14 changes: 13 additions & 1 deletion src/datachain/lib/dc.py
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Original file line number Diff line number Diff line change
Expand Up @@ -981,10 +981,22 @@ def _extend_to_data_model(self, method_name, *args, **kwargs):

@resolve_columns
def order_by(self, *args, descending: bool = False) -> "Self":
"""Orders by specified set of signals.
"""Orders by specified set of columns.

Parameters:
descending (bool): Whether to sort in descending order or not.

Example:
```py
dc.order_by("similarity_score", descending=True).limit(10)
```

Note:
Order is not guaranteed when steps are added after an `order_by` statement.
I.e. when using `from_dataset` an `order_by` statement should be used if
the order of the records in the chain is important.
Using `order_by` directly before `limit` will give expected results.
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I assume collect, show, to_parquet - are not considered as steps and will give also a "desired" output?

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collect - should but not guranteed (explanation in the original ticket #477)
show - yes
to_parquet - should but not guaranteed (uses collect_flatten)

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yep, probably needs to be a separate ticket then - e.g. combine things like order_by().collect() into a single statement, wdyt? (can be / should be implemented separately)

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Do you mean adding methods like collect_ordered OR adding an explicit order_by param to those methods or patching those functions? Is there a specific use case we're targeting or are we just trying to avoid confusion?

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I think it's a basic expectation that if you do order_by().collect() that you are getting a sorted result? collect is a way to iterate on the results I guess.

I mean that collect probably should be implemented similar to show() - something like ``order_by().collect()` should be a single SQL query probably

See https://github.com/iterative/datachain/issues/477 for further details.
"""
if descending:
args = tuple(sqlalchemy.desc(a) for a in args)
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