Upgrading to Polars 0.55.2

CHANGELOG.md

@@ -15,6 +15,20 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Removed many of the `unsafe` calls on the Rust side of Explorer and also dropped calls
   to `rustler::wrapper` for [Rustler changes](https://github.com/rusterlium/rustler/pull/768).
 
+### Updated
+
+- Updated Polars to [v0.55.2](https://github.com/pola-rs/polars/releases/tag/rs-0.55.2)
+  and the Rust toolchain to `nightly-2026-04-01`.
+
+### Backwards incompatible changes
+
+- `Explorer.Series.ewm_standard_deviation/2` and `Explorer.Series.ewm_variance/2` return
+  `nil` instead of `0.0` for the first value when `bias: false` (the default).
+- `Explorer.Series.covariance/2` returns `0.0` instead of `nil` for series with a single element.
+- The `:dtypes` option of the CSV readers is only applied by column name. Previously, when
+  all columns were given, names that didn't match the header were applied by position and
+  renamed the columns.
+
 ## [v0.12.0] - 2026-07-05
 
 ### Updated

README.md

@@ -233,13 +233,13 @@ Rust is going to be installed in the first compilation of the project. Otherwise
 install the correct version:
 
 ```sh
-rustup toolchain install nightly-2025-06-23
+rustup toolchain install nightly-2026-04-01
 ```
 
 You can also use [asdf](https://asdf-vm.com/):
 
 ```sh
-asdf install rust nightly-2025-06-23
+asdf install rust nightly-2026-04-01
 ```
 
 It's possible that you may need to install [`CMake`](https://cmake.org/) in order to build the project,

lib/explorer/series.ex

@@ -5450,14 +5450,14 @@ defmodule Explorer.Series do
       iex> Explorer.Series.ewm_standard_deviation(s)
       #Explorer.Series<
         Polars[5]
-        f64 [0.0, 0.7071067811865476, 0.9636241116594315, 1.1771636613972953, 1.3452425132127066]
+        f64 [nil, 0.7071067811865476, 0.9636241116594315, 1.1771636613972953, 1.3452425132127066]
       >
 
       iex> s = 1..5 |> Enum.to_list() |> Explorer.Series.from_list()
       iex> Explorer.Series.ewm_standard_deviation(s, alpha: 0.1)
       #Explorer.Series<
         Polars[5]
-        f64 [0.0, 0.7071067811865476, 0.999077064870281, 1.2879021599718157, 1.5741638698820741]
+        f64 [nil, 0.7071067811865476, 0.999077064870281, 1.2879021599718157, 1.5741638698820741]
       >
   """
   @doc type: :window
@@ -5505,14 +5505,14 @@ defmodule Explorer.Series do
       iex> Explorer.Series.ewm_variance(s)
       #Explorer.Series<
         Polars[5]
-        f64 [0.0, 0.5, 0.9285714285714286, 1.3857142857142861, 1.8096774193548393]
+        f64 [nil, 0.5, 0.9285714285714286, 1.3857142857142861, 1.8096774193548393]
       >
 
       iex> s = 1..5 |> Enum.to_list() |> Explorer.Series.from_list()
       iex> Explorer.Series.ewm_variance(s, alpha: 0.1)
       #Explorer.Series<
         Polars[5]
-        f64 [0.0, 0.5000000000000001, 0.9981549815498157, 1.658691973660068, 2.477991889242108]
+        f64 [nil, 0.5000000000000001, 0.9981549815498157, 1.658691973660068, 2.477991889242108]
       >
   """
   @doc type: :window