diff --git a/crates/fidc-core/src/data.rs b/crates/fidc-core/src/data.rs
index 4fe5fcf..ccf2fa9 100644
--- a/crates/fidc-core/src/data.rs
+++ b/crates/fidc-core/src/data.rs
@@ -87,6 +87,15 @@ pub enum DataSetError {
     DuplicateIntradayMarketOverlay { date: NaiveDate, symbol: String },
     #[error("cannot mutate shared {component} while finalizing a backtest dataset")]
     SharedComponentMutation { component: &'static str },
+    #[error(
+        "{kind} snapshot rows and symbol ids are misaligned on {date}: rows={row_count}, ids={symbol_id_count}"
+    )]
+    SnapshotSymbolIndexAlignment {
+        kind: &'static str,
+        date: NaiveDate,
+        row_count: usize,
+        symbol_id_count: usize,
+    },
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -1780,43 +1789,88 @@ impl DataSet {
             .into_iter()
             .map(|instrument| (instrument.symbol.clone(), instrument))
             .collect::<HashMap<_, _>>();
-        let mut market_rows_by_symbol = AHashMap::<String, Vec<&DailyMarketSnapshot>>::new();
-        for row in market_by_date.values().flatten() {
-            if let Some(rows) = market_rows_by_symbol.get_mut(row.symbol.as_str()) {
-                rows.push(row);
-                continue;
+        let symbol_id_by_code = build_symbol_id_index(
+            &instruments,
+            &market_by_date,
+            &factor_by_date,
+            &candidate_by_date,
+        );
+        let symbol_count = symbol_id_by_code.len();
+        let mut symbol_by_id = vec![Arc::<str>::from(""); symbol_count];
+        for (symbol, symbol_id) in &symbol_id_by_code {
+            symbol_by_id[*symbol_id as usize] = Arc::<str>::from(symbol.as_str());
+        }
+        let mut instruments_by_symbol_id = vec![None; symbol_count];
+        for (symbol, instrument) in &instruments {
+            if let Some(symbol_id) = symbol_id_by_code.get(symbol).copied() {
+                instruments_by_symbol_id[symbol_id as usize] = Some(instrument.clone());
             }
-            market_rows_by_symbol.insert(row.symbol.clone(), vec![row]);
         }
-        let market_rows_by_symbol = market_rows_by_symbol.into_iter().collect::<Vec<_>>();
-        let market_series_by_symbol = market_rows_by_symbol
+        let market_symbol_ids_by_date =
+            build_group_symbol_ids(&market_by_date, &symbol_id_by_code, |item| {
+                item.symbol.as_str()
+            });
+        let factor_symbol_ids_by_date =
+            build_group_symbol_ids(&factor_by_date, &symbol_id_by_code, |item| {
+                item.symbol.as_str()
+            });
+        let candidate_symbol_ids_by_date =
+            build_group_symbol_ids(&candidate_by_date, &symbol_id_by_code, |item| {
+                item.symbol.as_str()
+            });
+
+        let market_rows_by_symbol_id = group_rows_by_symbol_id(
+            "market",
+            &market_by_date,
+            &market_symbol_ids_by_date,
+            symbol_count,
+        )?;
+        let market_series_by_symbol_id = market_rows_by_symbol_id
             .into_par_iter()
-            .map(|(symbol, rows)| {
-                let series = Arc::new(SymbolPriceSeries::from_sorted_rows(symbol.clone(), rows));
-                (symbol, series)
+            .enumerate()
+            .map(|(symbol_id, rows)| {
+                (!rows.is_empty()).then(|| {
+                    Arc::new(SymbolPriceSeries::from_sorted_rows(
+                        symbol_by_id[symbol_id].to_string(),
+                        rows,
+                    ))
+                })
+            })
+            .collect::<Vec<_>>();
+        let market_series_by_symbol = market_series_by_symbol_id
+            .iter()
+            .enumerate()
+            .filter_map(|(symbol_id, series)| {
+                series.as_ref().map(|series| {
+                    (symbol_by_id[symbol_id].to_string(), Arc::clone(series))
+                })
             })
-            .collect::<Vec<_>>()
-            .into_iter()
             .collect::<AHashMap<_, _>>();
-        let mut factor_rows_by_symbol = AHashMap::<&str, Vec<&DailyFactorSnapshot>>::new();
-        for row in factor_by_date.values().flatten() {
-            factor_rows_by_symbol
-                .entry(row.symbol.as_str())
-                .or_default()
-                .push(row);
-        }
-        let adjusted_close_series_by_symbol = market_series_by_symbol
+
+        let factor_rows_by_symbol_id = group_rows_by_symbol_id(
+            "factor",
+            &factor_by_date,
+            &factor_symbol_ids_by_date,
+            symbol_count,
+        )?;
+        let adjusted_close_series_by_symbol_id = market_series_by_symbol_id
             .par_iter()
-            .filter_map(|(symbol, market)| {
-                let factor_rows = factor_rows_by_symbol
-                    .get(symbol.as_str())
-                    .map(Vec::as_slice)
-                    .unwrap_or_default();
-                AdjustedCloseSeries::new(market, factor_rows)
-                    .map(|series| (symbol.clone(), Arc::new(series)))
+            .enumerate()
+            .map(|(symbol_id, market)| {
+                market.as_ref().and_then(|market| {
+                    AdjustedCloseSeries::new(market, &factor_rows_by_symbol_id[symbol_id])
+                        .map(Arc::new)
+                })
+            })
+            .collect::<Vec<_>>();
+        let adjusted_close_series_by_symbol = adjusted_close_series_by_symbol_id
+            .iter()
+            .enumerate()
+            .filter_map(|(symbol_id, series)| {
+                series.as_ref().map(|series| {
+                    (symbol_by_id[symbol_id].to_string(), Arc::clone(series))
+                })
             })
-            .collect::<Vec<_>>()
-            .into_iter()
             .collect::<AHashMap<_, _>>();
         let factor_texts = factor_texts
             .into_iter()
@@ -1835,63 +1889,23 @@ impl DataSet {
             .map(|item| ((item.date, item.symbol.clone(), item.field.clone()), item))
             .collect::<HashMap<_, _>>();
 
-        let symbol_id_by_code = build_symbol_id_index(
-            &instruments,
-            &market_by_date,
-            &factor_by_date,
-            &candidate_by_date,
-        );
-        let mut symbol_by_id = vec![Arc::<str>::from(""); symbol_id_by_code.len()];
-        for (symbol, symbol_id) in &symbol_id_by_code {
-            symbol_by_id[*symbol_id as usize] = Arc::<str>::from(symbol.as_str());
-        }
-        let mut instruments_by_symbol_id = vec![None; symbol_id_by_code.len()];
-        for (symbol, instrument) in &instruments {
-            if let Some(symbol_id) = symbol_id_by_code.get(symbol).copied() {
-                instruments_by_symbol_id[symbol_id as usize] = Some(instrument.clone());
-            }
-        }
-        let market_symbol_ids_by_date =
-            build_group_symbol_ids(&market_by_date, &symbol_id_by_code, |item| {
-                item.symbol.as_str()
-            });
-        let factor_symbol_ids_by_date =
-            build_group_symbol_ids(&factor_by_date, &symbol_id_by_code, |item| {
-                item.symbol.as_str()
-            });
         let factor_market_cap_order_by_date =
             build_factor_market_cap_order(&factor_by_date, &factor_symbol_ids_by_date);
-        let candidate_symbol_ids_by_date =
-            build_group_symbol_ids(&candidate_by_date, &symbol_id_by_code, |item| {
-                item.symbol.as_str()
-            });
         let market_row_positions_by_date = build_dense_row_positions(
             &market_by_date,
             &market_symbol_ids_by_date,
-            symbol_id_by_code.len(),
+            symbol_count,
         );
         let factor_row_positions_by_date = build_dense_row_positions(
             &factor_by_date,
             &factor_symbol_ids_by_date,
-            symbol_id_by_code.len(),
+            symbol_count,
         );
         let candidate_row_positions_by_date = build_dense_row_positions(
             &candidate_by_date,
             &candidate_symbol_ids_by_date,
-            symbol_id_by_code.len(),
+            symbol_count,
         );
-        let mut market_series_by_symbol_id = vec![None; symbol_id_by_code.len()];
-        for (symbol, series) in &market_series_by_symbol {
-            if let Some(symbol_id) = symbol_id_by_code.get(symbol).copied() {
-                market_series_by_symbol_id[symbol_id as usize] = Some(Arc::clone(series));
-            }
-        }
-        let mut adjusted_close_series_by_symbol_id = vec![None; symbol_id_by_code.len()];
-        for (symbol, series) in &adjusted_close_series_by_symbol {
-            if let Some(symbol_id) = symbol_id_by_code.get(symbol).copied() {
-                adjusted_close_series_by_symbol_id[symbol_id as usize] = Some(Arc::clone(series));
-            }
-        }
         let market_series_end_positions_by_calendar_index =
             build_calendar_series_end_positions(&market_series_by_symbol_id, &calendar);
         let execution_quotes_by_date = build_execution_quote_index(execution_quotes);
@@ -4493,6 +4507,34 @@ where
         .collect()
 }
 
+fn group_rows_by_symbol_id<'a, T>(
+    kind: &'static str,
+    groups: &'a BTreeMap<NaiveDate, Vec<T>>,
+    symbol_ids_by_date: &BTreeMap<NaiveDate, Vec<u32>>,
+    symbol_count: usize,
+) -> Result<Vec<Vec<&'a T>>, DataSetError> {
+    let mut rows_by_symbol_id = (0..symbol_count)
+        .map(|_| Vec::<&T>::new())
+        .collect::<Vec<_>>();
+    for (date, rows) in groups {
+        let symbol_ids = symbol_ids_by_date
+            .get(date)
+            .expect("daily snapshot symbol ids must exist before series grouping");
+        if rows.len() != symbol_ids.len() {
+            return Err(DataSetError::SnapshotSymbolIndexAlignment {
+                kind,
+                date: *date,
+                row_count: rows.len(),
+                symbol_id_count: symbol_ids.len(),
+            });
+        }
+        for (row, symbol_id) in rows.iter().zip(symbol_ids) {
+            rows_by_symbol_id[*symbol_id as usize].push(row);
+        }
+    }
+    Ok(rows_by_symbol_id)
+}
+
 fn build_factor_market_cap_order(
     factor_by_date: &BTreeMap<NaiveDate, Vec<DailyFactorSnapshot>>,
     factor_symbol_ids_by_date: &BTreeMap<NaiveDate, Vec<u32>>,