nushell/crates/nu-command/src/dataframe/eager/drop_nulls.rs

use nu_engine::CallExt;
use nu_protocol::{
    ast::Call,
    engine::{Command, EngineState, Stack},
    Category, Example, PipelineData, ShellError, Signature, Span, SyntaxShape, Type, Value,
};

use super::super::values::utils::convert_columns_string;
use super::super::values::{Column, NuDataFrame};

#[derive(Clone)]
pub struct DropNulls;

impl Command for DropNulls {
    fn name(&self) -> &str {
        "drop-nulls"
    }

    fn usage(&self) -> &str {
        "Drops null values in dataframe"
    }

    fn signature(&self) -> Signature {
        Signature::build(self.name())
            .optional(
                "subset",
                SyntaxShape::Table,
                "subset of columns to drop nulls",
            )
            .category(Category::Custom("dataframe".into()))
    }

    fn examples(&self) -> Vec<Example> {
        vec![
            Example {
                description: "drop null values in dataframe",
                example: r#"let df = ([[a b]; [1 2] [3 0] [1 2]] | into df);
    let res = ($df.b / $df.b);
    let a = ($df | with-column $res --name res);
    $a | drop-nulls"#,
                result: Some(
                    NuDataFrame::try_from_columns(vec![
                        Column::new(
                            "a".to_string(),
                            vec![Value::test_int(1), Value::test_int(1)],
                        ),
                        Column::new(
                            "b".to_string(),
                            vec![Value::test_int(2), Value::test_int(2)],
                        ),
                        Column::new(
                            "res".to_string(),
                            vec![Value::test_int(1), Value::test_int(1)],
                        ),
                    ])
                    .expect("simple df for test should not fail")
                    .into_value(Span::test_data()),
                ),
            },
            Example {
                description: "drop null values in dataframe",
                example: r#"let s = ([1 2 0 0 3 4] | into df);
    ($s / $s) | drop-nulls"#,
                result: Some(
                    NuDataFrame::try_from_columns(vec![Column::new(
                        "div_0_0".to_string(),
                        vec![
                            Value::test_int(1),
                            Value::test_int(1),
                            Value::test_int(1),
                            Value::test_int(1),
                        ],
                    )])
                    .expect("simple df for test should not fail")
                    .into_value(Span::test_data()),
                ),
            },
        ]
    }

    fn input_type(&self) -> Type {
        Type::Custom("dataframe".into())
    }

    fn output_type(&self) -> Type {
        Type::Custom("dataframe".into())
    }

    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 columns: Option<Vec<Value>> = call.opt(engine_state, stack, 0)?;

    let (subset, col_span) = match columns {
        Some(cols) => {
            let (agg_string, col_span) = convert_columns_string(cols, call.head)?;
            (Some(agg_string), col_span)
        }
        None => (None, call.head),
    };

    let subset_slice = subset.as_ref().map(|cols| &cols[..]);

    df.as_ref()
        .drop_nulls(subset_slice)
        .map_err(|e| {
            ShellError::GenericError(
                "Error dropping nulls".into(),
                e.to_string(),
                Some(col_span),
                None,
                Vec::new(),
            )
        })
        .map(|df| PipelineData::Value(NuDataFrame::dataframe_into_value(df, call.head), None))
}

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

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