group-by now returns a table instead of a record (#10848)

# Description

Previously `group-by` returned a record containing each group as a
column. This data layout is hard to work with for some tasks because you
have to further manipulate the result to do things like determine the
number of items in each group, or the number of groups. `transpose` will
turn the record returned by `group-by` into a table, but this is
expensive when `group-by` is run on a large input.

In a discussion with @fdncred [several
workarounds](https://github.com/nushell/nushell/discussions/10462) to
common tasks were discussed, but they seem unsatisfying in general.

Now when `group-by --to-table` is used a table is returned with the
columns "groups" and "items" making it easier to do things like count
the number of groups (`| length`) or count the number of items in each
group (`| each {|g| $g.items | length`)

# User-Facing Changes

* `group-by` returns a `table` with "group" and "items" columns instead
of a `record` with one column per group name

# Tests + Formatting

Tests for `group-by` were updated

# After Submitting

* No breaking changes were made. The new `--to-table` switch should be
added automatically to the [`group-by`
documentation](https://www.nushell.sh/commands/docs/group-by.html)

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

@@ -22,10 +22,15 @@ impl Command for GroupBy {
             // example. Perhaps Table should be a subtype of List, in which case
             // the current signature would suffice even when a Table example
             // exists.
-            .input_output_types(vec![(
+            .input_output_types(vec![
-                Type::List(Box::new(Type::Any)),
+                (Type::List(Box::new(Type::Any)), Type::Record(vec![])),
-                Type::Record(vec![]),
+                (Type::List(Box::new(Type::Any)), Type::Table(vec![])),
-            )])
+            ])
+            .switch(
+                "to-table",
+                "Return a table with \"groups\" and \"items\" columns",
+                None,
+            )
             .optional(
                 "grouper",
                 SyntaxShape::OneOf(vec![
@@ -80,7 +85,6 @@ impl Command for GroupBy {
                         ),
                 })),
             },
-
             Example {
                 description: "You can also group by raw values by leaving out the argument",
                 example: "['1' '3' '1' '3' '2' '1' '1'] | group-by",
@@ -101,6 +105,46 @@ impl Command for GroupBy {
                         ),
                 })),
             },
+            Example {
+                description: "You can also output a table instead of a record",
+                example: "['1' '3' '1' '3' '2' '1' '1'] | group-by --to-table",
+                result: Some(Value::test_list(vec![
+                    Value::test_record(
+                        record! {
+                            "group" => Value::test_string("1"),
+                            "items" => Value::test_list(
+                                vec![
+                                    Value::test_string("1"),
+                                    Value::test_string("1"),
+                                    Value::test_string("1"),
+                                    Value::test_string("1"),
+                                ]
+                            )
+                        }
+                    ),
+                    Value::test_record(
+                        record! {
+                            "group" => Value::test_string("3"),
+                            "items" => Value::test_list(
+                                vec![
+                                    Value::test_string("3"),
+                                    Value::test_string("3"),
+                                ]
+                            )
+                        }
+                    ),
+                    Value::test_record(
+                        record! {
+                            "group" => Value::test_string("2"),
+                            "items" => Value::test_list(
+                                vec![
+                                    Value::test_string("2"),
+                                ]
+                            )
+                        }
+                    ),
+                ])),
+            },
         ]
     }
 }
@@ -123,11 +167,11 @@ pub fn group_by(
         ));
     }
 
-    let group_value = match grouper {
+    let groups = match grouper {
         Some(v) => {
             let span = v.span();
             match v {
-                Value::CellPath { val, .. } => group_cell_path(val, values, span)?,
+                Value::CellPath { val, .. } => group_cell_path(val, values)?,
                 Value::Block { .. } | Value::Closure { .. } => {
                     let block: Option<Closure> = call.opt(engine_state, stack, 0)?;
                     group_closure(&values, span, block, stack, engine_state, call)?
@@ -141,17 +185,22 @@ pub fn group_by(
                 }
             }
         }
-        None => group_no_grouper(values, span)?,
+        None => group_no_grouper(values)?,
     };
 
-    Ok(PipelineData::Value(group_value, None))
+    let value = if call.has_flag("to-table") {
+        groups_to_table(groups, span)
+    } else {
+        groups_to_record(groups, span)
+    };
+
+    Ok(PipelineData::Value(value, None))
 }
 
 pub fn group_cell_path(
     column_name: CellPath,
     values: Vec<Value>,
-    span: Span,
+) -> Result<IndexMap<String, Vec<Value>>, ShellError> {
-) -> Result<Value, ShellError> {
     let mut groups: IndexMap<String, Vec<Value>> = IndexMap::new();
 
     for value in values.into_iter() {
@@ -167,16 +216,10 @@ pub fn group_cell_path(
         group.push(value);
     }
 
-    Ok(Value::record(
+    Ok(groups)
-        groups
-            .into_iter()
-            .map(|(k, v)| (k, Value::list(v, span)))
-            .collect(),
-        span,
-    ))
 }
 
-pub fn group_no_grouper(values: Vec<Value>, span: Span) -> Result<Value, ShellError> {
+pub fn group_no_grouper(values: Vec<Value>) -> Result<IndexMap<String, Vec<Value>>, ShellError> {
     let mut groups: IndexMap<String, Vec<Value>> = IndexMap::new();
 
     for value in values.into_iter() {
@@ -185,13 +228,7 @@ pub fn group_no_grouper(values: Vec<Value>, span: Span) -> Result<Value, ShellEr
         group.push(value);
     }
 
-    Ok(Value::record(
+    Ok(groups)
-        groups
-            .into_iter()
-            .map(|(k, v)| (k, Value::list(v, span)))
-            .collect(),
-        span,
-    ))
 }
 
 // TODO: refactor this, it's a bit of a mess
@@ -202,7 +239,7 @@ fn group_closure(
     stack: &mut Stack,
     engine_state: &EngineState,
     call: &Call,
-) -> Result<Value, ShellError> {
+) -> Result<IndexMap<String, Vec<Value>>, ShellError> {
     let error_key = "error";
     let mut keys: Vec<Result<String, ShellError>> = vec![];
     let value_list = Value::list(values.to_vec(), span);
@@ -268,13 +305,35 @@ fn group_closure(
         group.push(value);
     }
 
-    Ok(Value::record(
+    Ok(groups)
+}
+
+fn groups_to_record(groups: IndexMap<String, Vec<Value>>, span: Span) -> Value {
+    Value::record(
         groups
             .into_iter()
             .map(|(k, v)| (k, Value::list(v, span)))
             .collect(),
         span,
-    ))
+    )
+}
+
+fn groups_to_table(groups: IndexMap<String, Vec<Value>>, span: Span) -> Value {
+    Value::list(
+        groups
+            .into_iter()
+            .map(|(group, items)| {
+                Value::record(
+                    record! {
+                        "group" => Value::string(group, span),
+                        "items" => Value::list(items, span),
+                    },
+                    span,
+                )
+            })
+            .collect(),
+        span,
+    )
 }
 
 #[cfg(test)]

crates/nu-std/std/testing.nu

@@ -72,11 +72,10 @@ def create-test-record [] nothing -> record<before-each: string, after-each: str
             valid-annotations
             | get $x.annotation
         }
-        | group-by annotation
+        | group-by --to-table annotation
-        | transpose key value
+        | update items {|x|
-        | update value {|x|
+            $x.items.function_name
-            $x.value.function_name
+            | if $x.group in ["test", "test-skip"] {
-            | if $x.key in ["test", "test-skip"] {
                 $in
             } else {
                 get 0