port over the drop command from nushell (#358)

crates/nu-command/src/default_context.rs

@@ -40,6 +40,7 @@ pub fn create_default_context() -> EngineState {
             Def,
             Describe,
             Do,
+            Drop,
             Each,
             Echo,
             ExportCommand,

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

@@ -0,0 +1,109 @@
+use nu_engine::CallExt;
+
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{
+    Category, Example, IntoInterruptiblePipelineData, PipelineData, ShellError, Signature, Span,
+    SyntaxShape, Value,
+};
+use std::convert::TryInto;
+
+#[derive(Clone)]
+pub struct Drop;
+
+impl Command for Drop {
+    fn name(&self) -> &str {
+        "drop"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("drop")
+            .optional(
+                "rows",
+                SyntaxShape::Int,
+                "starting from the back, the number of rows to remove",
+            )
+            .category(Category::Filters)
+    }
+
+    fn usage(&self) -> &str {
+        "Remove the last number of rows or columns."
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![
+            Example {
+                example: "[0,1,2,3] | drop",
+                description: "Remove the last item of a list/table",
+                result: Some(Value::List {
+                    vals: vec![Value::test_int(0), Value::test_int(1), Value::test_int(2)],
+                    span: Span::unknown(),
+                }),
+            },
+            Example {
+                example: "[0,1,2,3] | drop 0",
+                description: "Remove zero item of a list/table",
+                result: Some(Value::List {
+                    vals: vec![
+                        Value::test_int(0),
+                        Value::test_int(1),
+                        Value::test_int(2),
+                        Value::test_int(3),
+                    ],
+                    span: Span::unknown(),
+                }),
+            },
+            Example {
+                example: "[0,1,2,3] | drop 2",
+                description: "Remove the last two items of a list/table",
+                result: Some(Value::List {
+                    vals: vec![Value::test_int(0), Value::test_int(1)],
+                    span: Span::unknown(),
+                }),
+            },
+        ]
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        call: &Call,
+        input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        let rows: Option<i64> = call.opt(engine_state, stack, 0)?;
+        let v: Vec<_> = input.into_iter().collect();
+        let vlen: i64 = v.len() as i64;
+
+        let rows_to_drop = if let Some(quantity) = rows {
+            quantity
+        } else {
+            1
+        };
+
+        if rows_to_drop == 0 {
+            Ok(v.into_iter().into_pipeline_data(engine_state.ctrlc.clone()))
+        } else {
+            let k = if vlen < rows_to_drop {
+                0
+            } else {
+                vlen - rows_to_drop
+            };
+
+            let iter = v.into_iter().take(k.try_into().unwrap());
+            Ok(iter.into_pipeline_data(engine_state.ctrlc.clone()))
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_examples() {
+        use crate::test_examples;
+
+        test_examples(Drop {})
+    }
+}

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

@@ -0,0 +1,3 @@
+pub mod command;
+
+pub use command::Drop;

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

@@ -1,5 +1,6 @@
 mod append;
 mod collect;
+mod drop;
 mod each;
 mod first;
 mod get;
@@ -18,6 +19,7 @@ mod zip;
 
 pub use append::Append;
 pub use collect::Collect;
+pub use drop::*;
 pub use each::Each;
 pub use first::First;
 pub use get::Get;