log-compaction.js

const events = ref([]);

// Map() of targetId -> event list
const targetEvents = computed(() => events.value
    .filter(it => it.targetId !== undefined)
    .reduce((ax, row) => ax.update(row.targetId, new List(),
                                   items => items.push(row)),
            new Map()));

const compacted = computed(() => {
  const ax = [];
  const visited = new Set();
  events.value.forEach(row => {
    if (row.task === undefined) {
      // root/global scope
      ax.push(row)
    } else {
      // target scope
      if (visited.has(row.targetId)) continue;
      visited.add(row.targetId);
      ax.push({targetId: row.targetId,
               events: targetEvents.get(row.targetId).get('events').toArray()});
    }
  });
  return ax;
})