Countries beginning with...

$10.$

Group countries according to the first letter of the name. As shown. Only give $"$U$"$ through to $"$Z$".$

You will need to use the $substr function and the $push aggregate function$\mathrm{.}1*$ db$.$world.aggregate$([2$ v $\{$$project: $\{3\_$id: $\text{'}$$name',$4$ startswith: $\{$$substr: $[\text{'}$$name', $0,1]\}5\}\}6$ v $\{$$match: $\{7\_$id: $\{$$gte: $\text{'}$U$\text{'}\}8\}3\}9\{$$sort: $\{\_$id: $1\}\}$