diff --git a/crates/fidc-core/src/data.rs b/crates/fidc-core/src/data.rs
index f31911d..58d9370 100644
--- a/crates/fidc-core/src/data.rs
+++ b/crates/fidc-core/src/data.rs
@@ -1,6 +1,7 @@
 use std::collections::{BTreeMap, HashMap, HashSet};
 use std::fs;
 use std::path::Path;
+use std::sync::Arc;
 
 use chrono::{NaiveDate, NaiveDateTime};
 use serde::{Deserialize, Serialize};
@@ -955,12 +956,12 @@ pub struct DataSet {
     calendar: TradingCalendar,
     market_by_date: BTreeMap<NaiveDate, Vec<DailyMarketSnapshot>>,
     market_index: HashMap<(NaiveDate, String), DailyMarketSnapshot>,
-    factor_by_date: BTreeMap<NaiveDate, Vec<DailyFactorSnapshot>>,
-    factor_index: HashMap<(NaiveDate, String), DailyFactorSnapshot>,
+    factor_by_date: BTreeMap<NaiveDate, Vec<Arc<DailyFactorSnapshot>>>,
+    factor_index: HashMap<(NaiveDate, String), Arc<DailyFactorSnapshot>>,
     factor_text_by_date: BTreeMap<NaiveDate, Vec<FactorTextValue>>,
     factor_text_index: HashMap<(NaiveDate, String, String), FactorTextValue>,
-    candidate_by_date: BTreeMap<NaiveDate, Vec<CandidateEligibility>>,
-    candidate_index: HashMap<(NaiveDate, String), CandidateEligibility>,
+    candidate_by_date: BTreeMap<NaiveDate, Vec<Arc<CandidateEligibility>>>,
+    candidate_index: HashMap<(NaiveDate, String), Arc<CandidateEligibility>>,
     corporate_actions_by_date: BTreeMap<NaiveDate, Vec<CorporateAction>>,
     execution_quotes_by_date: HashMap<NaiveDate, HashMap<String, Vec<IntradayExecutionQuote>>>,
     order_book_depth_index: HashMap<(NaiveDate, String), Vec<IntradayOrderBookDepthLevel>>,
@@ -1205,7 +1206,11 @@ impl DataSet {
     ) -> Result<Self, DataSetError> {
         let benchmark_code = collect_benchmark_code(&benchmarks)?;
         let calendar = TradingCalendar::new(benchmarks.iter().map(|item| item.date).collect());
-        let factors = normalize_factor_snapshots(factors);
+        let factors = normalize_factor_snapshots(factors)
+            .into_iter()
+            .map(Arc::new)
+            .collect::<Vec<_>>();
+        let candidates = candidates.into_iter().map(Arc::new).collect::<Vec<_>>();
 
         let instruments = instruments
             .into_iter()
@@ -1218,7 +1223,7 @@ impl DataSet {
             .map(|item| ((item.date, item.symbol.clone()), item))
             .collect::<HashMap<_, _>>();
 
-        let factor_by_date = group_by_date(factors.clone(), |item| item.date);
+        let factor_by_date = group_arc_by_date(&factors, |item| item.date);
         let factor_index = factors
             .into_iter()
             .map(|item| ((item.date, item.symbol.clone()), item))
@@ -1240,7 +1245,7 @@ impl DataSet {
             .map(|item| ((item.date, item.symbol.clone(), item.field.clone()), item))
             .collect::<HashMap<_, _>>();
 
-        let candidate_by_date = group_by_date(candidates.clone(), |item| item.date);
+        let candidate_by_date = group_arc_by_date(&candidates, |item| item.date);
         let candidate_index = candidates
             .into_iter()
             .map(|item| ((item.date, item.symbol.clone()), item))
@@ -1329,11 +1334,15 @@ impl DataSet {
     }
 
     pub fn factor(&self, date: NaiveDate, symbol: &str) -> Option<&DailyFactorSnapshot> {
-        self.factor_index.get(&(date, symbol.to_string()))
+        self.factor_index
+            .get(&(date, symbol.to_string()))
+            .map(Arc::as_ref)
     }
 
     pub fn candidate(&self, date: NaiveDate, symbol: &str) -> Option<&CandidateEligibility> {
-        self.candidate_index.get(&(date, symbol.to_string()))
+        self.candidate_index
+            .get(&(date, symbol.to_string()))
+            .map(Arc::as_ref)
     }
 
     pub fn benchmark(&self, date: NaiveDate) -> Option<&BenchmarkSnapshot> {
@@ -2089,7 +2098,7 @@ impl DataSet {
     pub fn factor_snapshots_on(&self, date: NaiveDate) -> Vec<&DailyFactorSnapshot> {
         self.factor_by_date
             .get(&date)
-            .map(|rows| rows.iter().collect())
+            .map(|rows| rows.iter().map(Arc::as_ref).collect())
             .unwrap_or_default()
     }
 
@@ -2110,7 +2119,7 @@ impl DataSet {
     pub fn candidate_snapshots_on(&self, date: NaiveDate) -> Vec<&CandidateEligibility> {
         self.candidate_by_date
             .get(&date)
-            .map(|rows| rows.iter().collect())
+            .map(|rows| rows.iter().map(Arc::as_ref).collect())
             .unwrap_or_default()
     }
 
@@ -2123,11 +2132,15 @@ impl DataSet {
             date,
             benchmark,
             market: self.market_by_date.get(&date).cloned().unwrap_or_default(),
-            factors: self.factor_by_date.get(&date).cloned().unwrap_or_default(),
+            factors: self
+                .factor_by_date
+                .get(&date)
+                .map(|rows| rows.iter().map(|row| row.as_ref().clone()).collect())
+                .unwrap_or_default(),
             candidates: self
                 .candidate_by_date
                 .get(&date)
-                .cloned()
+                .map(|rows| rows.iter().map(|row| row.as_ref().clone()).collect())
                 .unwrap_or_default(),
             corporate_actions: self
                 .corporate_actions_by_date
@@ -2200,7 +2213,9 @@ impl DataSet {
             .iter()
             .map(|day| {
                 evaluator(
-                    self.candidate_index.get(&(*day, symbol.to_string())),
+                    self.candidate_index
+                        .get(&(*day, symbol.to_string()))
+                        .map(Arc::as_ref),
                     self.market_index.get(&(*day, symbol.to_string())),
                 )
             })
@@ -3375,6 +3390,20 @@ where
     grouped
 }
 
+fn group_arc_by_date<T, F>(rows: &[Arc<T>], mut date_of: F) -> BTreeMap<NaiveDate, Vec<Arc<T>>>
+where
+    F: FnMut(&T) -> NaiveDate,
+{
+    let mut grouped = BTreeMap::<NaiveDate, Vec<Arc<T>>>::new();
+    for row in rows {
+        grouped
+            .entry(date_of(row.as_ref()))
+            .or_default()
+            .push(Arc::clone(row));
+    }
+    grouped
+}
+
 fn collect_benchmark_code(benchmarks: &[BenchmarkSnapshot]) -> Result<String, DataSetError> {
     let mut codes = benchmarks
         .iter()
@@ -3523,8 +3552,8 @@ fn build_order_book_depth_index(
 }
 
 fn build_eligible_universe(
-    factor_by_date: &BTreeMap<NaiveDate, Vec<DailyFactorSnapshot>>,
-    candidate_index: &HashMap<(NaiveDate, String), CandidateEligibility>,
+    factor_by_date: &BTreeMap<NaiveDate, Vec<Arc<DailyFactorSnapshot>>>,
+    candidate_index: &HashMap<(NaiveDate, String), Arc<CandidateEligibility>>,
     market_index: &HashMap<(NaiveDate, String), DailyMarketSnapshot>,
     instruments: &HashMap<String, Instrument>,
 ) -> BTreeMap<NaiveDate, Vec<EligibleUniverseSnapshot>> {