Port the every command (#626)

crates/nu-command/src/default_context.rs

@@ -59,6 +59,7 @@ pub fn create_default_context() -> EngineState {
             DropNth,
             Each,
             Empty,
+            Every,
             First,
             Flatten,
             Get,

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

@@ -0,0 +1,96 @@
+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,
+};
+
+#[derive(Clone)]
+pub struct Every;
+
+impl Command for Every {
+    fn name(&self) -> &str {
+        "every"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("every")
+            .required(
+                "stride",
+                SyntaxShape::Int,
+                "how many rows to skip between (and including) each row returned",
+            )
+            .switch(
+                "skip",
+                "skip the rows that would be returned, instead of selecting them",
+                Some('s'),
+            )
+            .category(Category::Filters)
+    }
+
+    fn usage(&self) -> &str {
+        "Show (or skip) every n-th row, starting from the first one."
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![
+            Example {
+                example: "[1 2 3 4 5] | every 2",
+                description: "Get every second row",
+                result: Some(Value::List {
+                    vals: vec![Value::test_int(1), Value::test_int(3), Value::test_int(5)],
+                    span: Span::test_data(),
+                }),
+            },
+            Example {
+                example: "[1 2 3 4 5] | every 2 --skip",
+                description: "Skip every second row",
+                result: Some(Value::List {
+                    vals: vec![Value::test_int(2), Value::test_int(4)],
+                    span: Span::test_data(),
+                }),
+            },
+        ]
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        call: &Call,
+        input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        let stride = match call.req::<usize>(engine_state, stack, 0)? {
+            0 => 1,
+            stride => stride,
+        };
+
+        let skip = call.has_flag("skip");
+
+        Ok(input
+            .into_iter()
+            .enumerate()
+            .filter_map(move |(i, value)| {
+                if (i % stride != 0) == skip {
+                    Some(value)
+                } else {
+                    None
+                }
+            })
+            .into_pipeline_data(engine_state.ctrlc.clone()))
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_examples() {
+        use crate::test_examples;
+
+        test_examples(Every {})
+    }
+}

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

@@ -7,6 +7,7 @@ mod compact;
 mod drop;
 mod each;
 mod empty;
+mod every;
 mod first;
 mod flatten;
 mod get;
@@ -38,6 +39,7 @@ pub use compact::Compact;
 pub use drop::*;
 pub use each::Each;
 pub use empty::Empty;
+pub use every::Every;
 pub use first::First;
 pub use flatten::Flatten;
 pub use get::Get;