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deanm0000 committed Feb 13, 2024
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Polars expressions support NumPy [ufuncs](https://numpy.org/doc/stable/reference/ufuncs.html). See [here](https://numpy.org/doc/stable/reference/ufuncs.html#available-ufuncs)
for a list on all supported numpy functions. Additionally, SciPy offers a wide host of ufuncs. Specifically, the [scipy.special](https://docs.scipy.org/doc/scipy/reference/special.html#module-scipy.special) namespace has ufunc versions of many (possibly most) of what is available under stats.

This means that if a function is not provided by Polars, we can use NumPy and we still have fast columnar operation through the NumPy API. ufuncs have a hook that diverts their own execution when one of its inputs is a class with the [__array_ufunc__](https://numpy.org/doc/stable/reference/arrays.classes.html#special-attributes-and-methods) method. Polars Expr class has this method which allows ufuncs to be input directly in a context (`select`, `with_columns`, `agg`) with relevant expressions as the input. This syntax extends even to multiple input functions.
This means that if a function is not provided by Polars, we can use NumPy and we still have fast columnar operation through the NumPy API. ufuncs have a hook that diverts their own execution when one of its inputs is a class with the [`__array_ufunc__`](https://numpy.org/doc/stable/reference/arrays.classes.html#special-attributes-and-methods) method. Polars Expr class has this method which allows ufuncs to be input directly in a context (`select`, `with_columns`, `agg`) with relevant expressions as the input. This syntax extends even to multiple input functions.

### Example

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### Note on Performance

The speed of ufuncs comes from being vectorized, and compiled. That said, there's no inherent benefit in using ufuncs just to avoid the use of `map_batches`. As mentioned above, ufuncs use a hook which gives polars the opportunity to run its own code before the ufunc is executed. In that way polars is still executing the ufunc with `map_batches`.
The speed of ufuncs comes from being vectorized, and compiled. That said, there's no inherent benefit in using ufuncs just to avoid the use of `map_batches`. As mentioned above, ufuncs use a hook which gives polars the opportunity to run its own code before the ufunc is executed. In that way polars is still executing the ufunc with `map_batches`.

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