Avoid copies in take_state

14% faster based on bench

Author: theirix

datafusion/functions-aggregate/src/first_last.rs

@@ -432,13 +432,9 @@ where
             EmitTo::First(n) => {
                 // split off the first N values in seen_values
                 //
-                // TODO make this more efficient rather than two
-                // copies and bitwise manipulation
-                let first_n: BooleanBuffer = bool_buf.iter().take(n).collect();
+                let first_n: BooleanBuffer = bool_buf.slice(0, n);
                 // reset the existing buffer
-                for b in bool_buf.iter().skip(n) {
-                    bool_buf_builder.append(b);
-                }
+                bool_buf_builder.append_buffer(&bool_buf.slice(n, bool_buf.len() - n));
                 first_n
             }
         }