nu-command 0.75.0

Nushell's built-in commands
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105

use super::super::values::{Column, NuDataFrame};
use nu_engine::CallExt;
use nu_protocol::{
    ast::Call,
    engine::{Command, EngineState, Stack},
    Category, Example, PipelineData, ShellError, Signature, Span, SyntaxShape, Type, Value,
};

#[derive(Clone)]
pub struct FirstDF;

impl Command for FirstDF {
    fn name(&self) -> &str {
        "first"
    }

    fn usage(&self) -> &str {
        "Show only the first number of rows."
    }

    fn signature(&self) -> Signature {
        Signature::build(self.name())
            .optional(
                "rows",
                SyntaxShape::Int,
                "starting from the front, the number of rows to return",
            )
            .input_type(Type::Custom("dataframe".into()))
            .output_type(Type::Custom("dataframe".into()))
            .category(Category::Custom("dataframe".into()))
    }

    fn examples(&self) -> Vec<Example> {
        vec![
            Example {
                description: "Return the first row of a dataframe",
                example: "[[a b]; [1 2] [3 4]] | into df | first",
                result: Some(
                    NuDataFrame::try_from_columns(vec![
                        Column::new("a".to_string(), vec![Value::test_int(1)]),
                        Column::new("b".to_string(), vec![Value::test_int(2)]),
                    ])
                    .expect("should not fail")
                    .into_value(Span::test_data()),
                ),
            },
            Example {
                description: "Return the first two rows of a dataframe",
                example: "[[a b]; [1 2] [3 4]] | into df | first 2",
                result: Some(
                    NuDataFrame::try_from_columns(vec![
                        Column::new(
                            "a".to_string(),
                            vec![Value::test_int(1), Value::test_int(3)],
                        ),
                        Column::new(
                            "b".to_string(),
                            vec![Value::test_int(2), Value::test_int(4)],
                        ),
                    ])
                    .expect("should not fail")
                    .into_value(Span::test_data()),
                ),
            },
        ]
    }

    fn run(
        &self,
        engine_state: &EngineState,
        stack: &mut Stack,
        call: &Call,
        input: PipelineData,
    ) -> Result<PipelineData, ShellError> {
        let df = NuDataFrame::try_from_pipeline(input, call.head)?;
        command(engine_state, stack, call, df)
    }
}

fn command(
    engine_state: &EngineState,
    stack: &mut Stack,
    call: &Call,
    df: NuDataFrame,
) -> Result<PipelineData, ShellError> {
    let rows: Option<usize> = call.opt(engine_state, stack, 0)?;
    let rows = rows.unwrap_or(1);

    let res = df.as_ref().head(Some(rows));
    Ok(PipelineData::Value(
        NuDataFrame::dataframe_into_value(res, call.head),
        None,
    ))
}

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

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