Adds drop number of rows command (#1663)

* Fix access to columns with quoted names

* Add a drop number of rows from end of table

crates/nu-cli/src/cli.rs

@@ -297,6 +297,7 @@ pub fn create_default_context(
             whole_stream_command(Last),
             whole_stream_command(Skip),
             whole_stream_command(Nth),
+            whole_stream_command(Drop),
             per_item_command(Format),
             per_item_command(Where),
             whole_stream_command(Compact),

crates/nu-cli/src/commands.rs

@@ -20,6 +20,7 @@ pub(crate) mod cp;
 pub(crate) mod date;
 pub(crate) mod debug;
 pub(crate) mod default;
+pub(crate) mod drop;
 pub(crate) mod du;
 pub(crate) mod each;
 pub(crate) mod echo;
@@ -129,6 +130,7 @@ pub(crate) use cp::Cpy;
 pub(crate) use date::Date;
 pub(crate) use debug::Debug;
 pub(crate) use default::Default;
+pub(crate) use drop::Drop;
 pub(crate) use du::Du;
 pub(crate) use each::Each;
 pub(crate) use echo::Echo;

crates/nu-cli/src/commands/drop.rs

@@ -0,0 +1,60 @@
+use crate::commands::WholeStreamCommand;
+use crate::context::CommandRegistry;
+use crate::prelude::*;
+use nu_errors::ShellError;
+use nu_protocol::{ReturnSuccess, Signature, SyntaxShape, Value};
+use nu_source::Tagged;
+
+pub struct Drop;
+
+#[derive(Deserialize)]
+pub struct DropArgs {
+    rows: Option<Tagged<u64>>,
+}
+
+impl WholeStreamCommand for Drop {
+    fn name(&self) -> &str {
+        "drop"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("drop").optional(
+            "rows",
+            SyntaxShape::Number,
+            "starting from the back, the number of rows to drop",
+        )
+    }
+
+    fn usage(&self) -> &str {
+        "Drop the last number of rows."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        args.process(registry, drop)?.run()
+    }
+}
+
+fn drop(DropArgs { rows }: DropArgs, context: RunnableContext) -> Result<OutputStream, ShellError> {
+    let stream = async_stream! {
+        let v: Vec<_> = context.input.into_vec().await;
+
+        let rows_to_drop = if let Some(quantity) = rows {
+            *quantity as usize
+        } else {
+            1
+        };
+
+        if rows_to_drop < v.len() {
+            let k = v.len() - rows_to_drop;
+            for x in v[0..k].iter() {
+                let y: Value = x.clone();
+                yield ReturnSuccess::value(y)
+            }
+        }
+    };
+    Ok(stream.to_output_stream())
+}

crates/nu-cli/tests/commands/drop.rs

@@ -0,0 +1,11 @@
+use nu_test_support::nu;
+
+#[test]
+fn drop_rows() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats",
+        r#"echo '[{"foo": 3}, {"foo": 8}, {"foo": 4}]' | from-json | drop 2 | get foo | sum | echo $it"#
+    );
+
+    assert_eq!(actual, "3");
+}

crates/nu-cli/tests/commands/mod.rs

@@ -5,6 +5,7 @@ mod cd;
 mod compact;
 mod cp;
 mod default;
+mod drop;
 mod each;
 mod edit;
 mod enter;