```ts
export function indexMap(labels: string[]): Record<string, number[]> {
  const result: Record<string, number[]> = {};
  for (let i = 0; i < labels.length; i++) {
    if (!result[labels[i]]) {
      result[labels[i]] = [];
    }
    result[labels[i]].push(i);
  }
  return result;
}
```