Added dataframe powers and demo image

README.org

@@ -0,0 +1,4 @@
+* Abacus
+
+[[abacus_demo.png]]
+

abacus-core/src/dataframe.rs

@@ -37,6 +37,8 @@ pub fn setup_engine(engine: &mut rhai::Engine) {
     engine.register_fn("-", script_functions::subtract_series_i64);
     engine.register_fn("-", script_functions::subtract_series_f64);
 
+    engine.register_fn("**", script_functions::power_series_f64);
+    engine.register_fn("**", script_functions::power_series_i64);
     engine.register_fn("*", script_functions::multiply_series_series);
     engine.register_fn("*", script_functions::multiply_series_i64);
     engine.register_fn("*", script_functions::multiply_series_f64);
@@ -283,6 +285,34 @@ mod script_functions {
         Series(a.0 - b.0)
     }
 
+    pub fn power_series_i64(a: Series, b: i64) -> ScriptResult<Series> {
+        let name = a.name();
+        let a_series = a.0.clone();
+        let df = a_series
+            .into_frame()
+            .lazy()
+            .select([polars::prelude::col(name).pow(b)])
+            .collect()
+            .map_err(|e| e.to_string())?;
+        let s = df.column(name).map_err(|e| e.to_string())?;
+
+        Ok(Series(s.clone()))
+    }
+
+    pub fn power_series_f64(a: Series, b: f64) -> ScriptResult<Series> {
+        let name = a.name();
+        let a_series = a.0.clone();
+        let df = a_series
+            .into_frame()
+            .lazy()
+            .select([polars::prelude::col(name).pow(b)])
+            .collect()
+            .map_err(|e| e.to_string())?;
+        let s = df.column(name).map_err(|e| e.to_string())?;
+
+        Ok(Series(s.clone()))
+    }
+
     pub fn multiply_series_i64(a: Series, b: i64) -> Series {
         Series(a.0 * b)
     }