Dataframe with real index (#5892)

* remove extra print

* dataframe with real index

* corrected dataframe tests

* clippy error

* clippy error

crates/nu-command/src/dataframe/eager/to_nu.rs

@@ -34,15 +34,20 @@ impl Command for ToNu {
     }
 
     fn examples(&self) -> Vec<Example> {
-        let cols = vec!["a".into(), "b".into()];
+        let cols = vec!["index".into(), "a".into(), "b".into()];
         let rec_1 = Value::Record {
             cols: cols.clone(),
-            vals: vec![Value::test_int(1), Value::test_int(2)],
+            vals: vec![Value::test_int(0), Value::test_int(1), Value::test_int(2)],
             span: Span::test_data(),
         };
         let rec_2 = Value::Record {
+            cols: cols.clone(),
+            vals: vec![Value::test_int(1), Value::test_int(3), Value::test_int(4)],
+            span: Span::test_data(),
+        };
+        let rec_3 = Value::Record {
             cols,
-            vals: vec![Value::test_int(3), Value::test_int(4)],
+            vals: vec![Value::test_int(2), Value::test_int(3), Value::test_int(4)],
             span: Span::test_data(),
         };
 
@@ -51,7 +56,7 @@ impl Command for ToNu {
                 description: "Shows head rows from dataframe",
                 example: "[[a b]; [1 2] [3 4]] | into df | into nu",
                 result: Some(Value::List {
-                    vals: vec![rec_1, rec_2.clone()],
+                    vals: vec![rec_1, rec_2],
                     span: Span::test_data(),
                 }),
             },
@@ -59,7 +64,7 @@ impl Command for ToNu {
                 description: "Shows tail rows from dataframe",
                 example: "[[a b]; [1 2] [5 6] [3 4]] | into df | into nu -t -n 1",
                 result: Some(Value::List {
-                    vals: vec![rec_2],
+                    vals: vec![rec_3],
                     span: Span::test_data(),
                 }),
             },

crates/nu-command/src/dataframe/values/nu_dataframe/conversion.rs

@@ -555,6 +555,12 @@ pub fn add_separator(values: &mut Vec<Value>, df: &DataFrame, span: Span) {
     let mut cols = vec![];
     let mut vals = vec![];
 
+    cols.push("index".to_string());
+    vals.push(Value::String {
+        val: "...".into(),
+        span,
+    });
+
     for name in df.get_column_names() {
         cols.push(name.to_string());
         vals.push(Value::String {

crates/nu-command/src/dataframe/values/nu_dataframe/mod.rs

@@ -400,10 +400,16 @@ impl NuDataFrame {
 
         let values = (0..size)
             .into_iter()
-            .map(|_| {
+            .map(|i| {
                 let mut cols = vec![];
                 let mut vals = vec![];
 
+                cols.push("index".into());
+                vals.push(Value::Int {
+                    val: (i + from_row) as i64,
+                    span,
+                });
+
                 for (name, col) in &mut iterators {
                     cols.push(name.clone());
 

crates/nu-command/src/viewers/table.rs

@@ -17,6 +17,7 @@ use terminal_size::{Height, Width};
 
 const STREAM_PAGE_SIZE: usize = 1000;
 const STREAM_TIMEOUT_CHECK_INTERVAL: usize = 100;
+const INDEX_COLUMN_NAME: &str = "index";
 
 fn get_width_param(width_param: Option<i64>) -> usize {
     if let Some(col) = width_param {
@@ -41,6 +42,10 @@ impl Command for Table {
         "Render the table."
     }
 
+    fn extra_usage(&self) -> &str {
+        "If the table contains a column called 'index', this column is used as the table index instead of the usual continuous index"
+    }
+
     fn search_terms(&self) -> Vec<&str> {
         vec!["display", "render"]
     }
@@ -374,8 +379,22 @@ fn convert_to_table(
             // String1 = datatype, String2 = value as string
             let mut row: Vec<(String, String)> = vec![];
             if !disable_index {
-                row = vec![("string".to_string(), (row_num + row_offset).to_string())];
+                let row_val = match &item {
+                    Value::Record { .. } => item
+                        .get_data_by_key(INDEX_COLUMN_NAME)
+                        .map(|value| value.into_string("", config)),
+                    _ => None,
                 }
+                .unwrap_or_else(|| (row_num + row_offset).to_string());
+                row = vec![("string".to_string(), (row_val).to_string())];
+            }
+
+            // The header with the INDEX is removed from the table headers since
+            // it is added to the natural table index
+            headers = headers
+                .into_iter()
+                .filter(|header| header != INDEX_COLUMN_NAME)
+                .collect();
 
             if headers.is_empty() {
                 row.push((