You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: sort_by_expr.rs
    path of file: ./repos/nushell/crates/nu-cmd-dataframe/src/dataframe/lazy
    
    the code of the file until where you have to start completion: use super::super::values::NuLazyFrame;
use crate::dataframe::values::{Column, NuDataFrame, NuExpression};
use nu_engine::CallExt;
u
    
    fn signature(&self) -> Signature {
        Signature::build(self.name())
            .rest(
                "sort expression",
                SyntaxShape::Any,
                "sort expression for the dataframe",
            )
            .named(
                "reverse",
                SyntaxShape::List(Box::new(SyntaxShape::Boolean)),
                "Reverse sorting. Default is false",
                Some('r'),
            )
            .switch(
                "nulls-last",
                "nulls are shown last in the dataframe",
                Some('n'),
            )
            .switch("maintain-order", "Maintains order during sort", Some('m'))
            .input_output_type(
                Type::Custom("dataframe".into()),
                Type::Custom("dataframe".into()),
            )
            .category(Category::Custom("lazyframe".into()))
    }