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docs: Correct the definition of an expression in the user guide #14750

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Mar 21, 2024
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docs: Correct the definition of an expression in the user guide #14750

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92feac4
correct expressions definition
MarcoGorelli Feb 28, 2024
6d5d499
Merge remote-tracking branch 'upstream/main' into expressions
MarcoGorelli Mar 3, 2024
5f648b9
use definition from definitive guide
MarcoGorelli Mar 3, 2024
6160f68
reduce
MarcoGorelli Mar 3, 2024
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8 changes: 7 additions & 1 deletion docs/user-guide/concepts/expressions.md
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Expand Up @@ -21,7 +21,13 @@ Polars performs these core data transformations very quickly by:
- automatic query optimization on each expression
- automatic parallelization of expressions on many columns

Polars expressions are a mapping from a series to a series (or mathematically `Fn(Series) -> Series`). As expressions have a `Series` as an input and a `Series` as an output then it is straightforward to do a sequence of expressions (similar to method chaining in pandas).
An expression is a tree of operations that describe how to construct one or more
Series. As the outputs are Series, it is straightforward to
apply a sequence of expressions (similar to method chaining in pandas) each of which
transforms the output from the previous step.

If this seems abstract and confusing - don't worry! People quickly develop an intuition for expressions
just by looking at a few examples. We'll do that next!

## Examples

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