Merge pull request #280 from jonathandturner/nth

Add nth command

README.md

@@ -155,6 +155,7 @@ Nu adheres closely to a set of goals that make up its design philosophy. As feat
 | edit field value | Edit an existing field to have a new value |
 | skip amount | Skip a number of rows |
 | first amount | Show only the first number of rows |
+| nth row-number | Return only the selected row |
 | str (field) | Apply string function. Optional use the field of a table |
 | tags | Read the tags (metadata) for values |
 | to-array | Collapse rows into a single list |

src/cli.rs

@@ -158,6 +158,7 @@ pub async fn cli() -> Result<(), Box<dyn Error>> {
             command("size", Box::new(size::size)),
             command("from-yaml", Box::new(from_yaml::from_yaml)),
             command("enter", Box::new(enter::enter)),
+            command("nth", Box::new(nth::nth)),
             command("n", Box::new(next::next)),
             command("p", Box::new(prev::prev)),
             command("lines", Box::new(lines::lines)),

src/commands.rs

@@ -24,6 +24,7 @@ crate mod lines;
 crate mod ls;
 crate mod mkdir;
 crate mod next;
+crate mod nth;
 crate mod open;
 crate mod pick;
 crate mod plugin;

src/commands/first.rs

@@ -2,8 +2,6 @@ use crate::errors::ShellError;
 use crate::parser::CommandRegistry;
 use crate::prelude::*;
 
-// TODO: "Amount remaining" wrapper
-
 pub fn first(args: CommandArgs, registry: &CommandRegistry) -> Result<OutputStream, ShellError> {
     let args = args.evaluate_once(registry)?;
 

src/commands/nth.rs

@@ -0,0 +1,32 @@
+use crate::errors::ShellError;
+use crate::parser::CommandRegistry;
+use crate::prelude::*;
+
+pub fn nth(args: CommandArgs, registry: &CommandRegistry) -> Result<OutputStream, ShellError> {
+    let args = args.evaluate_once(registry)?;
+
+    if args.len() == 0 {
+        return Err(ShellError::labeled_error(
+            "Nth requires an amount",
+            "needs amount",
+            args.name_span(),
+        ));
+    }
+
+    let amount = args.expect_nth(0)?.as_i64();
+
+    let amount = match amount {
+        Ok(o) => o,
+        Err(_) => {
+            return Err(ShellError::labeled_error(
+                "Value is not a number",
+                "expected integer",
+                args.expect_nth(0)?.span(),
+            ))
+        }
+    };
+
+    Ok(OutputStream::from_input(
+        args.input.values.skip(amount as u64).take(1),
+    ))
+}