mongo aggregation query

gistfile1.json

[
	{
		$match: 
		{
			"last_request.2015_05_20": {$exists: true}
		}
	},
	{
		$project: {
			"main_computer": 1,
			"client_type": 1,
			"showcase_code": 1,
			"download_speed.main": { $ifNull : [ "$download_speed.main", [ 0 ] ] },
			"download_speed.site": { $ifNull: ["$download_speed.site", [0] ] }
		}
	},
	{
		$unwind: "$download_speed.main"
	},
	{
		$unwind: "$download_speed.site"
	},
	{
		$group: { 
			"_id":  "$showcase_code",
			"main_speed_count": {
				$sum: {
					$cond: {
						if : { $gt: ["$download_speed.main", 0] },
						then: 1,
						else: 0
					}
				}
			},
			"main_speed_sum": {
				$sum: "$download_speed.main"
			},
			"site_speed_count": {
				$sum: {
					$cond: {
						if : { $gt: ["$download_speed.site", 0] },
						then: 1,
						else: 0
					}
				}
			},
			"site_speed_sum": {
				$sum: "$download_speed.site"
			},
			"total_main": {
				$sum: "$main_computer"
			},
			"total_windows":  {
				$sum: {
					$cond: {
						if : {$eq: ["$client_type", "WIN"]},
						then: 1,
						else: 0
					}
				}
			},
			"total_android":  {
				$sum: {
					$cond: {
						if : { $eq: ["$client_type", "ANDRO"] },
						then: 1,
						else: 0
					}
				}
			},
			"total": {
				$sum: 1
			}
		}
	},
	{
		$project: {
			"main_speed_count": 1,
			"main_speed_sum": 1,
			"site_speed_count": 1,
			"site_speed_sum": 1,
			"showcase_code": 1,
			"total_main": 1,
			"total_windows": 1,
			"total_android": 1,
			"total_windows2": {$subtract: ["$total_windows", "$total_main"] },
			"total_main": 1,
			"total_other": { $subtract: [{$subtract: ["$total", "$total_windows"]}, "$total_android"] },
			"total": 1
		}
	},
	{
		$project: {
			"avg_speed_main": {$cond: {
				if: { $gt: ["$main_speed_count", 0] },
				then:  { $divide: ["$main_speed_sum", "$main_speed_count"] },
				else: 0
			} },
			"avg_speed_site": {$cond: {
				if: { $gt: ["$site_speed_count", 0] },
				then:  { $divide: ["$site_speed_sum", "$site_speed_count"] },
				else: 0
			} },
			"showcase_code": 1,
			"total_main": 1,
			"total_windows": 1,
			"total_android": 1,
			"total_windows2": 1,
			"total_main": 1,
			"total_other": 1,
			"total": 1
		}
	},
	{
		$sort: {
			"_id": 1
		}
	}
]