MAPREDUCE Tutorial - Revision history

40166222: Provided a much better target answer for Q8.

2019-02-06T20:19:46Z

Provided a much better target answer for Q8.

← Older revision		Revision as of 20:19, 6 February 2019
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	{out: {inline: 1}}		{out: {inline: 1}}
	);</nowiki></pre>		);</nowiki></pre>
	<pre class="ans"><nowiki>db.world.mapReduce(function(){~~if(~~this.capital){emit((this.capital~~).substring(~~0~~,1)~~,{first:this.capital,last:this.capital})}},function(_,v){~~let r={first:'ZZZ',last:'AAA',count:0};for(let i=0;~~i<v.~~length;~~i++){~~if(r~~.first~~>v[~~i].first){r.first=v[i].first~~};if(r.~~last<v[i].~~last){r.last=v[i~~].~~last};r.~~count~~+=1}~~		<pre class="ans"><nowiki>db.world.mapReduce(function(){this.capital&&emit(this.capital[0],{first:this.capital,last:this.capital,count:1})},function(t,i){return i.sort(function(t,i){return t.first<i.first?-1:1}),{first:i[0].first,last:i[i.length-1].first,count:i.length}},{out:{inline:1}});</nowiki></pre>
	~~return r},{finalize~~:~~function(_,v){if(!v~~.~~count){v.count=1~~}
	~~return v~~},out:{inline:1}});</nowiki></pre>
	</div>		</div>

2018-10-17T14:48:12Z

← Older revision		Revision as of 14:48, 17 October 2018
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	</div>		</div>
	<div class="q" data-lang="mongo">		<div class="q" data-lang="mongo">
	<p class="strong">For each letter in the alphabet find the amount of cities that start with that letter ~~as well as~~ the cities that come first and last alphabetically for that letter. e.g.</p>		<p class="strong">For each letter in the alphabet find the amount of cities that start with that letter. <br/>
			Additionally, find the two cities that come first and last alphabetically for that letter. e.g.</p>
	<syntaxhighlight lang="JavaScript">		<syntaxhighlight lang="JavaScript">
	{		{

2018-10-17T14:47:33Z

← Older revision		Revision as of 14:47, 17 October 2018
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	</div>		</div>
	<div class="q" data-lang="mongo">		<div class="q" data-lang="mongo">
	<p class="strong">For each letter in the alphabet, find the amount of cities ~~and~~ the cities that come first and last alphabetically. e.g.</p>		<p class="strong">For each letter in the alphabet find the amount of cities that start with that letter as well as the cities that come first and last alphabetically for that letter. e.g.</p>
	<syntaxhighlight lang="JavaScript">		<syntaxhighlight lang="JavaScript">
	{		{

2018-10-17T14:46:43Z

← Older revision		Revision as of 14:46, 17 October 2018
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	<div class="q" data-lang="mongo">		<div class="q" data-lang="mongo">
	<p class="strong">For each letter in the alphabet, find the amount of cities and the cities that come first and last alphabetically. e.g.</p>		<p class="strong">For each letter in the alphabet, find the amount of cities and the cities that come first and last alphabetically. e.g.</p>
	<~~pre~~>		<syntaxhighlight lang="JavaScript">
	{		{
	"_id" : "B",		"_id" : "B",
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	}		}
	},		},
	</~~pre~~>		</syntaxhighlight>
	<pre class="def"><nowiki>		<pre class="def"><nowiki>
	db.world.mapReduce(		db.world.mapReduce(

2018-10-17T14:45:30Z

MapReduce - The Basics

← Older revision		Revision as of 14:45, 17 October 2018
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	It is recommended to have some familiarity with JavaScript before attempting the following questions:		It is recommended to have some familiarity with JavaScript before attempting the following questions:
	[[JavaScript:~~_Fundamentals~~]]<br/>		[[JavaScript: Fundamentals]]<br/>
	[https://developer.mozilla.org/bm/docs/Web/JavaScript JavaScript \| MDN]		[https://developer.mozilla.org/bm/docs/Web/JavaScript JavaScript \| MDN]
	<div class='extra_space' style='width:1em; height:6em;'></div></div>		<div class='extra_space' style='width:1em; height:6em;'></div></div>

2018-10-17T14:45:11Z

MapReduce - The Basics

← Older revision		Revision as of 14:45, 17 October 2018
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	==MapReduce - The Basics==		==MapReduce - The Basics==
	<p>This tutorial introduces the ~~<code>~~MapReduce~~</code>~~ command.</p>		<p>This tutorial introduces the '''MapReduce''' command.</p>
	[[MapReduce]] examples are available.		[[MapReduce]] examples are available.
	<div>The MapReduce function allows to functions to be applied over a collection. The two functions map and reduce are important because:		<div>The MapReduce function allows to functions to be applied over a collection. The two functions map and reduce are important because:

2018-10-01T10:25:54Z

MapReduce - The Basics

← Older revision		Revision as of 10:25, 1 October 2018
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	*They can be distributed effectively; you can share the work load among a number of processors and get your answer faster.		*They can be distributed effectively; you can share the work load among a number of processors and get your answer faster.

	It is recommended to have some familiarity with JavaScript before attempting the following questions: [https://developer.mozilla.org/bm/docs/Web/JavaScript JavaScript \| MDN]		It is recommended to have some familiarity with JavaScript before attempting the following questions:
			[[JavaScript:_Fundamentals]]<br/>
			[https://developer.mozilla.org/bm/docs/Web/JavaScript JavaScript \| MDN]
	<div class='extra_space' style='width:1em; height:6em;'></div></div>		<div class='extra_space' style='width:1em; height:6em;'></div></div>

2018-07-12T15:52:00Z

← Older revision		Revision as of 15:52, 12 July 2018
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	<pre class="def"><nowiki>		<pre class="def"><nowiki>
	db.world.mapReduce(		db.world.mapReduce(
	function(){		function () {
	emit(null, null);		emit(null, null);
	},		},
	function(k, v){		function (k, v) {
	return null;		return null;
	},		},
	{out:{inline:1}}		{out: {inline: 1}}
	);</nowiki></pre>		);</nowiki></pre>
	<pre class="ans"><nowiki>db.world.mapReduce(function(){if(this.capital){emit((this.capital).substring(0,1),{first:this.capital,last:this.capital})}},function(_,v){let r={first:'ZZZ',last:'AAA',count:0};for(let i=0;i<v.length;i++){if(r.first>v[i].first){r.first=v[i].first};if(r.last<v[i].last){r.last=v[i].last};r.count+=1}		<pre class="ans"><nowiki>db.world.mapReduce(function(){if(this.capital){emit((this.capital).substring(0,1),{first:this.capital,last:this.capital})}},function(_,v){let r={first:'ZZZ',last:'AAA',count:0};for(let i=0;i<v.length;i++){if(r.first>v[i].first){r.first=v[i].first};if(r.last<v[i].last){r.last=v[i].last};r.count+=1}

2018-07-12T15:50:27Z

2018-06-22T14:58:21Z

← Older revision		Revision as of 14:58, 22 June 2018
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	case p>15000000:emit("MORE THAN 15000000",1);break}},function(_,v){return Array.sum(v)},{out:{inline:1}});</nowiki></pre>		case p>15000000:emit("MORE THAN 15000000",1);break}},function(_,v){return Array.sum(v)},{out:{inline:1}});</nowiki></pre>
	</div>		</div>
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