nushell/crates/nu-command/src/commands/dataframe/select.rs

use crate::prelude::*;
use nu_engine::WholeStreamCommand;
use nu_errors::ShellError;
use nu_protocol::{dataframe::NuDataFrame, Signature, SyntaxShape, Value};

use super::utils::{convert_columns, parse_polars_error};

pub struct DataFrame;

impl WholeStreamCommand for DataFrame {
    fn name(&self) -> &str {
        "dataframe select"
    }

    fn usage(&self) -> &str {
        "Creates a new dataframe with the selected columns"
    }

    fn signature(&self) -> Signature {
        Signature::build("dataframe select").required(
            "columns",
            SyntaxShape::Table,
            "selected column names",
        )
    }

    fn run(&self, args: CommandArgs) -> Result<OutputStream, ShellError> {
        command(args)
    }

    fn examples(&self) -> Vec<Example> {
        vec![Example {
            description: "Create new dataframe with column a",
            example: "[[a b]; [1 2] [3 4]] | dataframe to-df | dataframe select [a]",
            result: None,
        }]
    }
}

fn command(mut args: CommandArgs) -> Result<OutputStream, ShellError> {
    let tag = args.call_info.name_tag.clone();

    let columns: Vec<Value> = args.req(0)?;

    let (col_string, col_span) = convert_columns(&columns, &tag)?;

    let df = NuDataFrame::try_from_stream(&mut args.input, &tag.span)?;

    let res = df
        .as_ref()
        .select(&col_string)
        .map_err(|e| parse_polars_error::<&str>(&e, &col_span, None))?;

    Ok(OutputStream::one(NuDataFrame::dataframe_to_value(res, tag)))
}