nushell/crates/nu-cmd-dataframe/src/dataframe/series/string/to_lowercase.rs

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

use nu_protocol::{
    ast::Call,
    engine::{Command, EngineState, Stack},
    Category, Example, PipelineData, ShellError, Signature, Span, Type, Value,
};
use polars::prelude::{IntoSeries, StringNameSpaceImpl};

#[derive(Clone)]
pub struct ToLowerCase;

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

    fn usage(&self) -> &str {
        "Lowercase the strings in the column."
    }

    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: "Modifies strings to lowercase",
            example: "[Abc aBc abC] | dfr into-df | dfr lowercase",
            result: Some(
                NuDataFrame::try_from_columns(vec![Column::new(
                    "0".to_string(),
                    vec![
                        Value::test_string("abc"),
                        Value::test_string("abc"),
                        Value::test_string("abc"),
                    ],
                )])
                .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 series = df.as_series(call.head)?;

    let casted = 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 mut res = casted.to_lowercase();
    res.rename(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(ToLowerCase {})])
    }
}