add coalesce for all backends #2647
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I'll probably need to write more tests, at the very least this should serve as a functional MVP. |
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Hold off on merging for now, I need some tests for coalescing across disparate datatypes. |
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@MarcoGorelli thoughts on the following considerations for
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thanks @camriddell !
i think what you've done is fine and we shouldn't do any casting on behalf of the user, let the backends handle that as they wish
narwhals/functions.py
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| flat_exprs = flatten( | ||
| [ | ||
| expr if isinstance(expr, (Expr, str)) else lit(expr) | ||
| for expr in chain(flatten([exprs]), more_exprs) | ||
| ] | ||
| ) |
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this looks a bit suspicious, can we reuse anything? check concat_str or any of the other functions in this file
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The main idea was to coerce any inputs that are not strings/expressions into literals. Though this would also mean that any valid nw.Series objects would be inappropriately coerced as well.
Is there a helper somewhere that does this? If not, I've made the change to remove this capability- reverting is easy.
narwhals/_duckdb/namespace.py
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| def coalesce(self, *exprs: DuckDBExpr) -> DuckDBExpr: | ||
| def func(df: DuckDBLazyFrame) -> list[Expression]: | ||
| cols = (c for _expr in exprs for c in _expr(df)) | ||
| return [CoalesceOperator(*cols)] | ||
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| return self._expr( | ||
| call=func, | ||
| evaluate_output_names=combine_evaluate_output_names(*exprs), | ||
| alias_output_names=combine_alias_output_names(*exprs), | ||
| backend_version=self._backend_version, | ||
| version=self._version, | ||
| ) |
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this should be elementwise, right? can we use the new _with_elementwise here for duckdb and pyspark?
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Adds a
narwhals.coalescefunction for use with Narwhals Expressions.