Failed to resolve polars_core, arrow::legacy, Dataframe is polars-lazy = "0.44.2"

Question

Despite the:

1. reading of the polar_lazy 0.44.2

2. sucessful installation of cargo add polars-lazy

the following code results in errors:

• error[E0433]: failed to resolve: could not find legacy in arrow

• error[E0433]: failed to resolve: use of undeclared crate or module polars_core

• error[E0412]: cannot find type PolarsResult in this scope

• error[E0412]: cannot find type DataFrame in this scope

  use polars_core::prelude::*;
  use polars_core::df;
  use polars_lazy::prelude::*;
  use arrow::legacy::prelude::QuantileMethod;
  
  fn main() {
    let test = example()
    println!("show dataframe: {:?}", test);
  
  }
  
  fn example() -> PolarsResult<DataFrame> {
   let df = df!(
       "date" => ["2020-08-21", "2020-08-21", "2020-08-22", "2020-08-23", "2020-08-22"],
       "temp" => [20, 10, 7, 9, 1],
       "rain" => [0.2, 0.1, 0.3, 0.1, 0.01]
   )?;
  
   df.lazy()
   .group_by([col("date")])
   .agg([
       col("rain").min().alias("min_rain"),
       col("rain").sum().alias("sum_rain"),
       col("rain").quantile(lit(0.5), QuantileMethod::Nearest).alias("median_rain"),
   ])
   .sort(["date"], Default::default())
   .collect()
  }
  

N.B: Cargo.toml

[dependencies]
arrow = "53.2.0"
polars-lazy = "0.44.2"

Answer 1

It's a little hard to tell, but the "arrow" crate used in the example is a renamed import of polars-arrow, not the arrow crate (see the dependencies in the Cargo.toml):

[dependencies.arrow]
default-features = false
features = ["compute_aggregate", "compute_arithmetics", "compute_bitwise", "compute_boolean", "compute_boolean_kleene", "compute_cast", "compute_comparison"]
package = "polars-arrow"
version = "0.44.2"

And it feels a little like stating the obvious, but to use polars_core you'll have to add polars-core to your dependencies.

So you should remove arrow = "53.2.0" from your dependencies and instead add:

polars-core = "0.44.2"
arrow = { version = "0.44.2", package = "polars-arrow" }