nu_command/filters/
headers.rs

1use nu_engine::command_prelude::*;
2use nu_protocol::{Config, shell_error::generic::GenericError};
3
4#[derive(Clone)]
5pub struct Headers;
6
7impl Command for Headers {
8    fn name(&self) -> &str {
9        "headers"
10    }
11
12    fn signature(&self) -> Signature {
13        Signature::build(self.name())
14            .input_output_types(vec![(Type::table(), Type::table())])
15            .category(Category::Filters)
16    }
17
18    fn description(&self) -> &str {
19        "Use the first row of the table as column names."
20    }
21
22    fn examples(&self) -> Vec<Example<'_>> {
23        vec![
24            Example {
25                description: "Sets the column names for a table created by `split column`",
26                example: r#""a b c|1 2 3" | split row "|" | split column " " | headers"#,
27                result: Some(Value::test_list(vec![Value::test_record(record! {
28                    "a" => Value::test_string("1"),
29                    "b" => Value::test_string("2"),
30                    "c" => Value::test_string("3"),
31                })])),
32            },
33            Example {
34                description: "Columns which don't have data in their first row are removed",
35                example: r#""a b c|1 2 3|1 2 3 4" | split row "|" | split column " " | headers"#,
36                result: Some(Value::test_list(vec![
37                    Value::test_record(record! {
38                        "a" => Value::test_string("1"),
39                        "b" => Value::test_string("2"),
40                        "c" => Value::test_string("3"),
41                    }),
42                    Value::test_record(record! {
43                        "a" => Value::test_string("1"),
44                        "b" => Value::test_string("2"),
45                        "c" => Value::test_string("3"),
46                    }),
47                ])),
48            },
49        ]
50    }
51
52    fn run(
53        &self,
54        engine_state: &EngineState,
55        stack: &mut Stack,
56        call: &Call,
57        input: PipelineData,
58    ) -> Result<PipelineData, ShellError> {
59        let mut input = input.into_stream_or_original(engine_state);
60        let config = &stack.get_config(engine_state);
61        let metadata = input.take_metadata();
62        let span = input.span().unwrap_or(call.head);
63        let value = input.into_value(span)?;
64        let Value::List { vals: table, .. } = value else {
65            return Err(ShellError::TypeMismatch {
66                err_message: "not a table".to_string(),
67                span,
68            });
69        };
70
71        let (old_headers, new_headers) = extract_headers(&table, span, config)?;
72        let value = replace_headers(table, span, &old_headers, &new_headers)?;
73
74        Ok(value.into_pipeline_data_with_metadata(metadata))
75    }
76}
77
78fn extract_headers(
79    table: &[Value],
80    span: Span,
81    config: &Config,
82) -> Result<(Vec<String>, Vec<String>), ShellError> {
83    let record = table
84        .first()
85        .ok_or_else(|| {
86            ShellError::Generic(GenericError::new(
87                "Found empty list",
88                "unable to extract headers",
89                span,
90            ))
91        })?
92        .as_record()?;
93
94    let new_headers = record
95        .values()
96        .enumerate()
97        .map(|(idx, value)| make_header_string(config, idx, value))
98        .collect::<Result<Vec<_>, _>>()?;
99
100    let old_headers = record.columns().cloned().collect();
101
102    Ok((old_headers, new_headers))
103}
104
105fn make_header_string(config: &Config, idx: usize, value: &Value) -> Result<String, ShellError> {
106    match value {
107        Value::Nothing { .. }
108        | Value::String { .. }
109        | Value::Bool { .. }
110        | Value::Float { .. }
111        | Value::Int { .. } => {
112            let col = value.to_expanded_string("", config);
113            Ok(match col.is_empty() {
114                true => format!("column{idx}"),
115                false => col,
116            })
117        }
118        _ => Err(ShellError::TypeMismatch {
119            err_message: "needs compatible type: Null, String, Bool, Float, Int".to_string(),
120            span: value.span(),
121        }),
122    }
123}
124
125fn replace_headers(
126    rows: Vec<Value>,
127    span: Span,
128    old_headers: &[String],
129    new_headers: &[String],
130) -> Result<Value, ShellError> {
131    rows.into_iter()
132        .skip(1)
133        .map(|value| {
134            let span = value.span();
135            if let Value::Record { val: record, .. } = value {
136                Ok(Value::record(
137                    record
138                        .into_owned()
139                        .into_iter()
140                        .filter_map(|(col, val)| {
141                            old_headers
142                                .iter()
143                                .position(|c| c == &col)
144                                .map(|i| (new_headers[i].clone(), val))
145                        })
146                        .collect(),
147                    span,
148                ))
149            } else {
150                Err(ShellError::CantConvert {
151                    to_type: "record".into(),
152                    from_type: value.get_type().to_string(),
153                    span,
154                    help: None,
155                })
156            }
157        })
158        .collect::<Result<_, _>>()
159        .map(|rows| Value::list(rows, span))
160}
161
162#[cfg(test)]
163mod test {
164    use super::*;
165
166    #[test]
167    fn test_examples() -> nu_test_support::Result {
168        nu_test_support::test().examples(Headers)
169    }
170}
nu_command/filters/headers.rs

nu_command/filters/
headers.rs
