nushell/crates/nu_plugin_polars/src/dataframe/lazy/explode.rs

use crate::dataframe::values::{Column, NuDataFrame, NuExpression, NuLazyFrame};
use crate::values::{CustomValueSupport, PolarsPluginObject};
use crate::PolarsPlugin;

use nu_plugin::{EngineInterface, EvaluatedCall, PluginCommand};
use nu_protocol::{
    Category, Example, LabeledError, PipelineData, ShellError, Signature, Span, SyntaxShape, Type,
    Value,
};

#[derive(Clone)]
pub struct LazyExplode;

impl PluginCommand for LazyExplode {
    type Plugin = PolarsPlugin;

    fn name(&self) -> &str {
        "polars explode"
    }

    fn usage(&self) -> &str {
        "Explodes a dataframe or creates a explode expression."
    }

    fn signature(&self) -> Signature {
        Signature::build(self.name())
            .rest(
                "columns",
                SyntaxShape::String,
                "columns to explode, only applicable for dataframes",
            )
            .input_output_types(vec![
                (
                    Type::Custom("expression".into()),
                    Type::Custom("expression".into()),
                ),
                (
                    Type::Custom("dataframe".into()),
                    Type::Custom("dataframe".into()),
                ),
            ])
            .category(Category::Custom("lazyframe".into()))
    }

    fn examples(&self) -> Vec<Example> {
        vec![
            Example {
                description: "Explode the specified dataframe",
                example: "[[id name hobbies]; [1 Mercy [Cycling Knitting]] [2 Bob [Skiing Football]]] | polars into-df | polars explode hobbies | polars collect",
                result: Some(
                    NuDataFrame::try_from_columns(vec![
                        Column::new(
                            "id".to_string(), 
                            vec![
                                Value::test_int(1),
                                Value::test_int(1),
                                Value::test_int(2),
                                Value::test_int(2),
                            ]),
                        Column::new(
                            "name".to_string(), 
                            vec![
                                Value::test_string("Mercy"),
                                Value::test_string("Mercy"),
                                Value::test_string("Bob"),
                                Value::test_string("Bob"),
                            ]),
                        Column::new(
                            "hobbies".to_string(), 
                            vec![
                                Value::test_string("Cycling"),
                                Value::test_string("Knitting"),
                                Value::test_string("Skiing"),
                                Value::test_string("Football"),
                            ]),
                    ], None)
                    .expect("simple df for test should not fail")
                    .into_value(Span::test_data()),
                )
            },
            Example {
                description: "Select a column and explode the values",
                example: "[[id name hobbies]; [1 Mercy [Cycling Knitting]] [2 Bob [Skiing Football]]] | polars into-df | polars select (polars col hobbies | polars explode)",
                result: Some(
                    NuDataFrame::try_from_columns(vec![
                        Column::new(
                            "hobbies".to_string(), 
                            vec![
                                Value::test_string("Cycling"),
                                Value::test_string("Knitting"),
                                Value::test_string("Skiing"),
                                Value::test_string("Football"),
                            ]),
                    ], None)
                   .expect("simple df for test should not fail")
                   .into_value(Span::test_data()),
                ),
            },
        ]
    }

    fn run(
        &self,
        plugin: &Self::Plugin,
        engine: &EngineInterface,
        call: &EvaluatedCall,
        input: PipelineData,
    ) -> Result<PipelineData, LabeledError> {
        explode(plugin, engine, call, input).map_err(LabeledError::from)
    }
}

pub(crate) fn explode(
    plugin: &PolarsPlugin,
    engine: &EngineInterface,
    call: &EvaluatedCall,
    input: PipelineData,
) -> Result<PipelineData, ShellError> {
    let value = input.into_value(call.head);

    match PolarsPluginObject::try_from_value(plugin, &value)? {
        PolarsPluginObject::NuDataFrame(df) => {
            let lazy = df.lazy();
            explode_lazy(plugin, engine, call, lazy)
        }
        PolarsPluginObject::NuLazyFrame(lazy) => explode_lazy(plugin, engine, call, lazy),
        PolarsPluginObject::NuExpression(expr) => explode_expr(plugin, engine, call, expr),
        _ => Err(ShellError::CantConvert {
            to_type: "dataframe or expression".into(),
            from_type: value.get_type().to_string(),
            span: call.head,
            help: None,
        }),
    }
}

pub(crate) fn explode_lazy(
    plugin: &PolarsPlugin,
    engine: &EngineInterface,
    call: &EvaluatedCall,
    lazy: NuLazyFrame,
) -> Result<PipelineData, ShellError> {
    let columns = call
        .positional
        .iter()
        .map(|e| e.as_str().map(|s| s.to_string()))
        .collect::<Result<Vec<String>, ShellError>>()?;

    let exploded = lazy
        .to_polars()
        .explode(columns.iter().map(AsRef::as_ref).collect::<Vec<&str>>());
    let lazy = NuLazyFrame::from(exploded);

    lazy.to_pipeline_data(plugin, engine, call.head)
}

pub(crate) fn explode_expr(
    plugin: &PolarsPlugin,
    engine: &EngineInterface,
    call: &EvaluatedCall,
    expr: NuExpression,
) -> Result<PipelineData, ShellError> {
    let expr: NuExpression = expr.into_polars().explode().into();
    expr.to_pipeline_data(plugin, engine, call.head)
}

#[cfg(test)]
mod test {
    use super::*;
    use crate::test::test_polars_plugin_command;

    #[test]
    fn test_examples() -> Result<(), ShellError> {
        test_polars_plugin_command(&LazyExplode)
    }
}