nushell/crates/nu-command/src/filters/select.rs

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

#[derive(Clone)]
pub struct Select;

impl Command for Select {
    fn name(&self) -> &str {
        "select"
    }

    fn signature(&self) -> Signature {
        Signature::build("select")
            .rest(
                "rest",
                SyntaxShape::CellPath,
                "the columns to select from the table",
            )
            .category(Category::Filters)
    }

    fn usage(&self) -> &str {
        "Down-select table to only these columns."
    }

    fn run(
        &self,
        engine_state: &EngineState,
        stack: &mut Stack,
        call: &Call,
        input: PipelineData,
    ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
        let columns: Vec<CellPath> = call.rest(engine_state, stack, 0)?;
        let span = call.head;

        select(engine_state, span, columns, input)
    }

    fn examples(&self) -> Vec<Example> {
        vec![
            Example {
                description: "Select just the name column",
                example: "ls | select name",
                result: None,
            },
            Example {
                description: "Select the name and size columns",
                example: "ls | select name size",
                result: None,
            },
        ]
    }
}

fn select(
    engine_state: &EngineState,
    span: Span,
    columns: Vec<CellPath>,
    input: PipelineData,
) -> Result<PipelineData, ShellError> {
    if columns.is_empty() {
        return Err(ShellError::CantFindColumn(span, span)); //FIXME?
    }

    match input {
        PipelineData::Value(
            Value::List {
                vals: input_vals,
                span,
            },
            ..,
        ) => {
            let mut output = vec![];

            for input_val in input_vals {
                let mut cols = vec![];
                let mut vals = vec![];
                for path in &columns {
                    //FIXME: improve implementation to not clone
                    let fetcher = input_val.clone().follow_cell_path(&path.members)?;

                    cols.push(path.into_string());
                    vals.push(fetcher);
                }

                output.push(Value::Record { cols, vals, span })
            }

            Ok(output
                .into_iter()
                .into_pipeline_data(engine_state.ctrlc.clone()))
        }
        PipelineData::ListStream(stream, ..) => Ok(stream
            .map(move |x| {
                let mut cols = vec![];
                let mut vals = vec![];
                for path in &columns {
                    //FIXME: improve implementation to not clone
                    match x.clone().follow_cell_path(&path.members) {
                        Ok(value) => {
                            cols.push(path.into_string());
                            vals.push(value);
                        }
                        Err(error) => {
                            cols.push(path.into_string());
                            vals.push(Value::Error { error });
                        }
                    }
                }

                Value::Record { cols, vals, span }
            })
            .into_pipeline_data(engine_state.ctrlc.clone())),
        PipelineData::Value(v, ..) => {
            let mut cols = vec![];
            let mut vals = vec![];

            for cell_path in columns {
                // FIXME: remove clone
                let result = v.clone().follow_cell_path(&cell_path.members)?;

                cols.push(cell_path.into_string());
                vals.push(result);
            }

            Ok(Value::Record { cols, vals, span }.into_pipeline_data())
        }
        _ => Ok(PipelineData::new(span)),
    }
}