diff --git a/frontend/src/lib/dataExport.js b/frontend/src/lib/dataExport.js
index 3158cbb..ee52e49 100644
--- a/frontend/src/lib/dataExport.js
+++ b/frontend/src/lib/dataExport.js
@@ -53,3 +53,62 @@ export function listExportableParams(dailyTemplate, statuses) {
 
   return params;
 }
+
+// A cell has a value unless it is null, undefined, or the empty string.
+// (0 and false are real values.)
+function hasValue(v) {
+  return v !== null && v !== undefined && v !== '';
+}
+
+function dateKey(date) {
+  return String(date).slice(0, 10); // ISO datetime or date → YYYY-MM-DD
+}
+
+// Pivot statuses into { columns, rows }.
+//   columns: [{ id, header }] — all animals, ordered by name, headers
+//            disambiguated with animal_id_string on duplicate names.
+//   rows:    [{ date, values }] — one per date that has ≥1 value; values are
+//            aligned to columns, blank cells are '' (empty string).
+export function buildMatrix(statuses, animals, param) {
+  const sortedAnimals = [...(animals ?? [])].sort((a, b) =>
+    String(a.animal_name ?? '').localeCompare(String(b.animal_name ?? '')),
+  );
+
+  const nameCounts = new Map();
+  for (const a of sortedAnimals) {
+    const n = a.animal_name ?? '';
+    nameCounts.set(n, (nameCounts.get(n) ?? 0) + 1);
+  }
+  const columns = sortedAnimals.map((a) => {
+    const name = a.animal_name ?? '';
+    const header = nameCounts.get(name) > 1 ? `${name} (${a.animal_id_string ?? ''})` : name;
+    return { id: a.id, header };
+  });
+  const colIndex = new Map(columns.map((c, i) => [c.id, i]));
+
+  // cells: dateKey -> Map(animalId -> value); first status per (date, animal) wins.
+  const cells = new Map();
+  const datesWithData = new Set();
+  const ordered = [...(statuses ?? [])].sort((a, b) => dateKey(a.date).localeCompare(dateKey(b.date)));
+  for (const s of ordered) {
+    if (!colIndex.has(s.animal_id)) continue;
+    const dk = dateKey(s.date);
+    if (!cells.has(dk)) cells.set(dk, new Map());
+    const byAnimal = cells.get(dk);
+    if (byAnimal.has(s.animal_id)) continue; // first wins
+    const v = extractValue(s, param);
+    byAnimal.set(s.animal_id, v);
+    if (hasValue(v)) datesWithData.add(dk);
+  }
+
+  const rows = [...datesWithData].sort().map((dk) => {
+    const byAnimal = cells.get(dk);
+    const values = columns.map((c) => {
+      const v = byAnimal.has(c.id) ? byAnimal.get(c.id) : null;
+      return hasValue(v) ? v : '';
+    });
+    return { date: dk, values };
+  });
+
+  return { columns, rows };
+}
diff --git a/frontend/tests/dataExport.test.js b/frontend/tests/dataExport.test.js
index e97f7f4..7be93a3 100644
--- a/frontend/tests/dataExport.test.js
+++ b/frontend/tests/dataExport.test.js
@@ -70,3 +70,58 @@ describe('listExportableParams', () => {
     expect(listExportableParams(undefined, undefined).length).toBe(2); // just the two fixed metrics
   });
 });
+
+import { buildMatrix } from '../src/lib/dataExport';
+
+const animals = [
+  { id: 'a2', animal_name: 'Beta', animal_id_string: 'R-002' },
+  { id: 'a1', animal_name: 'Alpha', animal_id_string: 'R-001' },
+];
+const totalParam = { kind: 'total' };
+
+describe('buildMatrix', () => {
+  it('orders columns by animal_name and rows by date ascending', () => {
+    const statuses = [
+      { animal_id: 'a1', date: '2026-07-02T00:00:00.000Z', analysis_summary: { total: 5 } },
+      { animal_id: 'a2', date: '2026-07-01T00:00:00.000Z', analysis_summary: { total: 9 } },
+    ];
+    const m = buildMatrix(statuses, animals, totalParam);
+    expect(m.columns.map((c) => c.header)).toEqual(['Alpha', 'Beta']);
+    expect(m.rows.map((r) => r.date)).toEqual(['2026-07-01', '2026-07-02']);
+    // Row for 07-01: Alpha blank, Beta 9
+    expect(m.rows[0].values).toEqual(['', 9]);
+    // Row for 07-02: Alpha 5, Beta blank
+    expect(m.rows[1].values).toEqual([5, '']);
+  });
+  it('includes only dates that have at least one value (0 counts as a value)', () => {
+    const statuses = [
+      { animal_id: 'a1', date: '2026-07-01T00:00:00.000Z', analysis_summary: { total: 0 } },
+      { animal_id: 'a1', date: '2026-07-03T00:00:00.000Z', analysis_summary: null }, // no value
+    ];
+    const m = buildMatrix(statuses, animals, totalParam);
+    expect(m.rows.map((r) => r.date)).toEqual(['2026-07-01']);
+    expect(m.rows[0].values).toEqual([0, '']);
+  });
+  it('disambiguates duplicate animal names with the id string', () => {
+    const dupAnimals = [
+      { id: 'a1', animal_name: 'Rat', animal_id_string: 'R-001' },
+      { id: 'a2', animal_name: 'Rat', animal_id_string: 'R-002' },
+    ];
+    const statuses = [{ animal_id: 'a1', date: '2026-07-01T00:00:00.000Z', analysis_summary: { total: 1 } }];
+    const m = buildMatrix(statuses, dupAnimals, totalParam);
+    expect(m.columns.map((c) => c.header)).toEqual(['Rat (R-001)', 'Rat (R-002)']);
+  });
+  it('keeps the first status when a subject has duplicates on one date', () => {
+    const statuses = [
+      { animal_id: 'a1', date: '2026-07-01T00:00:00.000Z', analysis_summary: { total: 7 } },
+      { animal_id: 'a1', date: '2026-07-01T00:00:00.000Z', analysis_summary: { total: 99 } },
+    ];
+    const m = buildMatrix(statuses, animals, totalParam);
+    expect(m.rows[0].values).toEqual([7, '']);
+  });
+  it('returns empty rows when no status has a value', () => {
+    const m = buildMatrix([{ animal_id: 'a1', date: '2026-07-01T00:00:00.000Z', analysis_summary: null }], animals, totalParam);
+    expect(m.rows).toEqual([]);
+    expect(m.columns.length).toBe(2);
+  });
+});