nu-cmd-dataframe 0.93.0

Nushell's dataframe commands based on polars.
Documentation 
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use crate::dataframe::values::{Column, NuDataFrame};
use nu_engine::command_prelude::*;

#[derive(Clone)]
pub struct DataTypes;

impl Command for DataTypes {
    fn name(&self) -> &str {
        "dfr dtypes"
    }

    fn usage(&self) -> &str {
        "Show dataframe data types."
    }

    fn signature(&self) -> Signature {
        Signature::build(self.name())
            .input_output_type(
                Type::Custom("dataframe".into()),
                Type::Custom("dataframe".into()),
            )
            .category(Category::Custom("dataframe".into()))
    }

    fn examples(&self) -> Vec<Example> {
        vec![Example {
            description: "Dataframe dtypes",
            example: "[[a b]; [1 2] [3 4]] | dfr into-df | dfr dtypes",
            result: Some(
                NuDataFrame::try_from_columns(
                    vec![
                        Column::new(
                            "column".to_string(),
                            vec![Value::test_string("a"), Value::test_string("b")],
                        ),
                        Column::new(
                            "dtype".to_string(),
                            vec![Value::test_string("i64"), Value::test_string("i64")],
                        ),
                    ],
                    None,
                )
                .expect("simple df for test should not fail")
                .into_value(Span::test_data()),
            ),
        }]
    }

    fn run(
        &self,
        engine_state: &EngineState,
        stack: &mut Stack,
        call: &Call,
        input: PipelineData,
    ) -> Result<PipelineData, ShellError> {
        command(engine_state, stack, call, input)
    }
}

fn command(
    _engine_state: &EngineState,
    _stack: &mut Stack,
    call: &Call,
    input: PipelineData,
) -> Result<PipelineData, ShellError> {
    let df = NuDataFrame::try_from_pipeline(input, call.head)?;

    let mut dtypes: Vec<Value> = Vec::new();
    let names: Vec<Value> = df
        .as_ref()
        .get_column_names()
        .iter()
        .map(|v| {
            let dtype = df
                .as_ref()
                .column(v)
                .expect("using name from list of names from dataframe")
                .dtype();

            let dtype_str = dtype.to_string();

            dtypes.push(Value::string(dtype_str, call.head));

            Value::string(*v, call.head)
        })
        .collect();

    let names_col = Column::new("column".to_string(), names);
    let dtypes_col = Column::new("dtype".to_string(), dtypes);

    NuDataFrame::try_from_columns(vec![names_col, dtypes_col], None)
        .map(|df| PipelineData::Value(df.into_value(call.head), None))
}

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

    #[test]
    fn test_examples() {
        test_dataframe(vec![Box::new(DataTypes {})])
    }
}