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::*;

use polars::{
    prelude::{IntoSeries, NamedFrom, StringNameSpaceImpl},
    series::Series,
};

#[derive(Clone)]
pub struct StrSlice;

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

    fn usage(&self) -> &str {
        "Slices the string from the start position until the selected length."
    }

    fn signature(&self) -> Signature {
        Signature::build(self.name())
            .required("start", SyntaxShape::Int, "start of slice")
            .named("length", SyntaxShape::Int, "optional length", Some('l'))
            .input_output_type(
                Type::Custom("dataframe".into()),
                Type::Custom("dataframe".into()),
            )
            .category(Category::Custom("dataframe".into()))
    }

    fn examples(&self) -> Vec<Example> {
        vec![
            Example {
                description: "Creates slices from the strings",
                example: "[abcded abc321 abc123] | dfr into-df | dfr str-slice 1 --length 2",
                result: Some(
                    NuDataFrame::try_from_columns(
                        vec![Column::new(
                            "0".to_string(),
                            vec![
                                Value::test_string("bc"),
                                Value::test_string("bc"),
                                Value::test_string("bc"),
                            ],
                        )],
                        None,
                    )
                    .expect("simple df for test should not fail")
                    .into_value(Span::test_data()),
                ),
            },
            Example {
                description: "Creates slices from the strings without length",
                example: "[abcded abc321 abc123] | dfr into-df | dfr str-slice 1",
                result: Some(
                    NuDataFrame::try_from_columns(
                        vec![Column::new(
                            "0".to_string(),
                            vec![
                                Value::test_string("bcded"),
                                Value::test_string("bc321"),
                                Value::test_string("bc123"),
                            ],
                        )],
                        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 start: i64 = call.req(engine_state, stack, 0)?;
    let start = Series::new("", &[start]);

    let length: Option<i64> = call.get_flag(engine_state, stack, "length")?;
    let length = match length {
        Some(v) => Series::new("", &[v as u64]),
        None => Series::new_null("", 1),
    };

    let df = NuDataFrame::try_from_pipeline(input, call.head)?;
    let series = df.as_series(call.head)?;

    let chunked = series.str().map_err(|e| ShellError::GenericError {
        error: "Error casting to string".into(),
        msg: e.to_string(),
        span: Some(call.head),
        help: Some("The str-slice command can only be used with string columns".into()),
        inner: vec![],
    })?;

    let res = chunked
        .str_slice(&start, &length)
        .map_err(|e| ShellError::GenericError {
            error: "Dataframe Error".into(),
            msg: e.to_string(),
            span: Some(call.head),
            help: None,
            inner: vec![],
        })?
        .with_name(series.name());

    NuDataFrame::try_from_series(vec![res.into_series()], call.head)
        .map(|df| PipelineData::Value(NuDataFrame::into_value(df, call.head), None))
}

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

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