Kristina Chodorow

> db.runCommand({aggregate: "posts", pipeline: [
{
   // extract the fields 
   $project: {
        title : 1,
        url : 1,
        comments : 1
    }
},
{
    // explode the "comments" array into separate documents
    $unwind: "$comments"
},
{
    // query like a boss
    $match: {comments.author : "Serious Cat"}
}]})

> db.runCommand({aggregate: "posts", pipeline: [
{
   // extract the fields
   $project: {
        title : 1,
        url : 1,
        comments : 1
    }
{
    // explode "comments" array into separate documents
    $unwind: "$comments"
},
{
    // sort newest first
    $sort: {
        "comments.date" : -1
    }
},
{
    // get the 10 newest
    $limit: 10
}]})

{
    "url" : "/blog/spam",
    "title" : "Rant about Spam",
    "comments" : [
        {text : "Where can I get discount Prada shoes?", ...},
        {text : "First!", ...},
        {text : "I hate spam, too!", ...},
        {text : "I love spam.", ...}
    ]
}

{
    "url" : "/blog/spam",
    "title" : "Rant about Spam",
    "comments" : [
        {text : "Where can I get discount Prada shoes?", ...},
    ]
}
{
    "url" : "/blog/spam",
    "title" : "Rant about Spam",
    "comments" : [
        {text : "First!", ...}
    ]
}
{
    "url" : "/blog/spam",
    "title" : "Rant about Spam",
    "comments" : [
        {text : "I hate spam, too!", ...}
    ]
},
{
    "url" : "/blog/spam",
    "title" : "Rant about Spam",
    "comments" : [
        {text : "I love spam.", ...}
    ]
}

> db.runCommand({aggregate: "posts", pipeline: [
{
   // extract the fields we'll need
   $project: {
        title : 1,
        url : 1,
        comments : 1
    }
},
{
    // explode "comments" array into separate documents
    $unwind: "$comments"
},
{
    // count up votes by author
    $group : {
        _id : "$comments.author",
        popularity : {$sum : "$comments.votes"}
    }
},
{
    // sort by the new popular field
    $sort: {
        "popularity" : -1
    }
}]})

$ mongoimport --db chess --collection fast_win games.json
connected to: 127.0.0.1
imported 1132 objects

> use chess
switched to db chess
> db.fast_win.count()
1132
> db.fast_win.findOne()
{
	"_id" : ObjectId("4ed3965bf86479436d6f1cd7"),
	"event" : "?",
	"site" : "?",
	"date" : "????.??.??",
	"round" : "?",
	"white" : "Gedult D",
	"black" : "Kohn V",
	"result" : "1-0",
	"eco" : "B33/09",
	"moves" : {
		"1" : {
			"white" : {
				"move" : "e4"
			},
			"black" : {
				"move" : "c5"
			}
		},
		"2" : {
			"white" : {
				"move" : "Nf3"
			},
			"black" : {
				"move" : "Nc6"
			}
		},
                ...
		"10" : {
			"white" : {
				"move" : "Qa4"
			}
		}
	}
}

> db.runCommand({aggregate : "fast_win", pipeline : [
... {
...    $group : {
...        _id : "$result",      // group by 'result' field
...        numGames : {$sum : 1} // add 1 for every document in the group
...    }
... }]})
{
	"result" : [
		{
			"_id" : "0-1",
			"numGames" : 435
		},
		{
			"_id" : "1-0",
			"numGames" : 697
		}
	],
	"ok" : 1
}

> db.runCommand({aggregate: "fast_win", pipeline: [
... // '$project' is used to extract all of white's opening moves
... {
...     $project : {
...         // extract moves.1.white.move into a new field, firstMove
...         firstMove : "$moves.1.white.move"
...     }
... },
... // use '$group' to calculate the number of times each move occurred
... {
...     $group : { 
...         _id : "$firstMove",
...         numGames : {$sum : 1}
...     }
... }]})
{
	"result" : [
		{
			"_id" : "d3",
			"numGames" : 2
		},
		{
			"_id" : "e4",
			"numGames" : 696
		},
		{
			"_id" : "b4",
			"numGames" : 17
		},
		{
			"_id" : "g3",
			"numGames" : 3
		},
		{
			"_id" : "e3",
			"numGames" : 2
		},
		{
			"_id" : "c4",
			"numGames" : 36
		},
		{
			"_id" : "b3",
			"numGames" : 4
		},
		{
			"_id" : "g4",
			"numGames" : 11
		},
		{
			"_id" : "h4",
			"numGames" : 1
		},
		{
			"_id" : "Nf3",
			"numGames" : 37
		},
		{
			"_id" : "f3",
			"numGames" : 1
		},
		{
			"_id" : "f4",
			"numGames" : 25
		},
		{
			"_id" : "Nc3",
			"numGames" : 14
		},
		{
			"_id" : "d4",
			"numGames" : 283
		}
	],
	"ok" : 1
}

> db.runCommand({aggregate: "fast_win", pipeline: [
... // extract the first move
... {
...    $project : {
...        firstMove : "$moves.1.white.move",
...        // create a new field, "win", which is 1 if white won and 0 if black won
...        win : {$cond : [
...            {$eq : ["$result", "1-0"]}, 1, 0
...        ]}
...    }
... },
... // group by the move and count up how many winning games used it
... {
...     $group : {
...         _id : "$firstMove",
...         numGames : {$sum : 1},
...         numWins : {$sum : "$win"}
...     }
... },
... // calculate the percent of games won with this starting move
... {
...     $project : {
...         _id : 1,
...         numGames : 1,
...         percentWins : {
...             $multiply : [100, {
...                 $divide : ["$numWins","$numGames"]
...             }]
...         }
...     }
... },
... // discard moves that were used in less than 10 games (probably not representative) 
... {
...     $match : {
...         numGames : {$gte : 10}
...     }
... },
... // order from worst to best
... {
...     $sort : {
...         percentWins : 1
...     }
... }]})
{
	"result" : [
		{
			"_id" : "f4",
			"numGames" : 25,
			"percentWins" : 24
		},
		{
			"_id" : "b4",
			"numGames" : 17,
			"percentWins" : 35.294117647058826
		},
		{
			"_id" : "c4",
			"numGames" : 36,
			"percentWins" : 50
		},
		{
			"_id" : "d4",
			"numGames" : 283,
			"percentWins" : 50.53003533568905
		},
		{
			"_id" : "g4",
			"numGames" : 11,
			"percentWins" : 63.63636363636363
		},
		{
			"_id" : "Nf3",
			"numGames" : 37,
			"percentWins" : 67.56756756756756
		},
		{
			"_id" : "e4",
			"numGames" : 696,
			"percentWins" : 68.24712643678161
		},
		{
			"_id" : "Nc3",
			"numGames" : 14,
			"percentWins" : 78.57142857142857
		}
	],
	"ok" : 1
}

> db.runCommand({aggregate: "fast_win", pipeline: [
... // extract the first move
... {
...    $project : {
...        firstMove : "$moves.1.black.move",
...        win : {$cond : [
...            {$eq : ["$result", "0-1"]}, 1, 0
...        ]}
...    }
... },
... // group by the move and count up how many winning games used it
... {
...     $group : {
...         _id : "$firstMove",
...         numGames : {$sum : 1},
...         numWins : {$sum : "$win"}
...     }
... },
... // calculate the percent of games won with this starting move
... {
...     $project : {
...         _id : 1,
...         numGames : 1,
...         percentWins : {
...             $multiply : [100, {
...                 $divide : ["$numWins","$numGames"]
...             }]
...         }
...     }
... },
... // discard moves that were used in less than 10 games (probably not representative) 
... {
...     $match : {
...         numGames : {$gte : 10}
...     }
... },
... // get the best and worst
... {
...     $group : {
...          _id : 1,
...          best : {$max : "$_id"},
...          worst : {$min : "$_id"}
...     }
... }]})
{
	"result" : [
		{
			"_id" : 1,
			"best" : "g6",
			"worst" : "Nc6"
		}
	],
	"ok" : 1
}