The polars solution I saw on reddit a few months ago is also super slow. I'm thinking it might be my macbook

rust/Cargo.toml

@@ -7,3 +7,4 @@ edition = "2021"
 
 [dependencies]
 hashbrown = "0.14.3"
+polars = { version = "0.36.2", features = ["csv", "lazy", "nightly", "streaming"]}

rust/src/bin/polars.rs

@@ -0,0 +1,35 @@
+use polars::prelude::*;
+use std::time::Instant;
+use std::vec;
+
+fn run_polars() -> Result<DataFrame, PolarsError> {
+    let now = Instant::now();
+
+    let f1: Field = Field::new("station", DataType::String);
+    let f2: Field = Field::new("measure", DataType::Float64);
+    let sc: Schema = Schema::from_iter(vec![f1, f2]);
+
+    let q = LazyCsvReader::new("../measurements.txt")
+        .has_header(false)
+        .with_schema(Some(Arc::new(sc)))
+        .with_separator(b';')
+        .finish()?
+        .group_by(vec![col("station")])
+        .agg(vec![
+            col("measure").alias("min").min(),
+            col("measure").alias("mean").mean(),
+            col("measure").alias("max").max(),
+        ])
+        .sort("station", Default::default())
+        .with_streaming(true);
+
+    let df = q.collect()?;
+
+    println!("Time={} μs", now.elapsed().as_micros());
+
+    Ok(df)
+}
+
+fn main() {
+    run_polars();
+}