port over from nushell drop nth (#498)

crates/nu-command/src/default_context.rs

@@ -51,6 +51,7 @@ pub fn create_default_context() -> EngineState {
             Collect,
             Drop,
             DropColumn,
+            DropNth,
             Each,
             First,
             Get,

crates/nu-command/src/filters/drop/mod.rs

@@ -1,5 +1,7 @@
 pub mod column;
 pub mod command;
+pub mod nth;
 
 pub use column::DropColumn;
 pub use command::Drop;
+pub use nth::DropNth;

crates/nu-command/src/filters/drop/nth.rs

@@ -0,0 +1,122 @@
+use nu_engine::CallExt;
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{
+    Category, Example, IntoInterruptiblePipelineData, PipelineData, PipelineIterator, ShellError,
+    Signature, Span, SyntaxShape, Value,
+};
+
+#[derive(Clone)]
+pub struct DropNth;
+
+impl Command for DropNth {
+    fn name(&self) -> &str {
+        "drop nth"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("drop nth")
+            .rest("rest", SyntaxShape::Int, "the number of the row to drop")
+            .category(Category::Filters)
+    }
+
+    fn usage(&self) -> &str {
+        "Drop the selected rows."
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![
+            Example {
+                example: "[sam,sarah,2,3,4,5] | drop nth 0 1 2",
+                description: "Drop the first, second, and third row",
+                result: Some(Value::List {
+                    vals: vec![Value::test_int(3), Value::test_int(4), Value::test_int(5)],
+                    span: Span::unknown(),
+                }),
+            },
+            Example {
+                example: "[0,1,2,3,4,5] | drop nth 0 1 2",
+                description: "Drop the first, second, and third row",
+                result: Some(Value::List {
+                    vals: vec![Value::test_int(3), Value::test_int(4), Value::test_int(5)],
+                    span: Span::unknown(),
+                }),
+            },
+            Example {
+                example: "[0,1,2,3,4,5] | drop nth 0 2 4",
+                description: "Drop rows 0 2 4",
+                result: Some(Value::List {
+                    vals: vec![Value::test_int(1), Value::test_int(3), Value::test_int(5)],
+                    span: Span::unknown(),
+                }),
+            },
+            Example {
+                example: "[0,1,2,3,4,5] | drop nth 2 0 4",
+                description: "Drop rows 2 0 4",
+                result: Some(Value::List {
+                    vals: vec![Value::test_int(1), Value::test_int(3), Value::test_int(5)],
+                    span: Span::unknown(),
+                }),
+            },
+        ]
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        call: &Call,
+        input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        let mut rows: Vec<usize> = call.rest(engine_state, stack, 0)?;
+        rows.sort_unstable();
+        let pipeline_iter: PipelineIterator = input.into_iter();
+
+        Ok(DropNthIterator {
+            input: pipeline_iter,
+            rows,
+            current: 0,
+        }
+        .into_pipeline_data(engine_state.ctrlc.clone()))
+    }
+}
+
+struct DropNthIterator {
+    input: PipelineIterator,
+    rows: Vec<usize>,
+    current: usize,
+}
+
+impl Iterator for DropNthIterator {
+    type Item = Value;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            if let Some(row) = self.rows.get(0) {
+                if self.current == *row {
+                    self.rows.remove(0);
+                    self.current += 1;
+                    let _ = self.input.next();
+                    continue;
+                } else {
+                    self.current += 1;
+                    return self.input.next();
+                }
+            } else {
+                return self.input.next();
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_examples() {
+        use crate::test_examples;
+
+        test_examples(DropNth {})
+    }
+}