Added math avg

Linting

Fix clippy warning

Fix list of records

crates/nu-command/src/math/avg.rs

@@ -0,0 +1,83 @@
+use crate::math::reducers::{reducer_for, Reduce};
+use crate::math::utils::run_with_function;
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{Example, PipelineData, ShellError, Signature, Span, Value};
+
+#[derive(Clone)]
+pub struct SubCommand;
+
+impl Command for SubCommand {
+    fn name(&self) -> &str {
+        "math avg"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("math avg")
+    }
+
+    fn usage(&self) -> &str {
+        "Finds the average of a list of numbers or tables"
+    }
+
+    fn run(
+        &self,
+        _engine_state: &EngineState,
+        _stack: &mut Stack,
+        call: &Call,
+        input: PipelineData,
+    ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
+        run_with_function(call, input, average)
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Get the average of a list of numbers",
+            example: "[-50 100.0 25] | math avg",
+            result: Some(Value::Float {
+                val: 25.0,
+                span: Span::unknown(),
+            }),
+        }]
+    }
+}
+
+pub fn average(values: &[Value], head: &Span) -> Result<Value, ShellError> {
+    let sum = reducer_for(Reduce::Summation);
+    let total = &sum(
+        Value::Int {
+            val: 0,
+            span: Span::unknown(),
+        },
+        values.to_vec(),
+    )?;
+    match total {
+        Value::Filesize { val, span } => Ok(Value::Filesize {
+            val: val / values.len() as i64,
+            span: *span,
+        }),
+        Value::Duration { val, span } => Ok(Value::Duration {
+            val: val / values.len() as i64,
+            span: *span,
+        }),
+        _ => total.div(
+            *head,
+            &Value::Int {
+                val: values.len() as i64,
+                span: *head,
+            },
+        ),
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_examples() {
+        use crate::test_examples;
+
+        test_examples(SubCommand {})
+    }
+}