Efficient Use of Dictionary using custom data type

	public class AppData
	{
	public List<Country> AllCountries { get; private set; }
	public Dictionary<CountryCode, Country> AllCountriesByKey { get; private set; }
	public void Initialize(string csvFilePath)
	{
	CsvReader reader = new CsvReader(csvFilePath);
	this.AllCountries = reader.ReadAllCountries().OrderBy(x => x.Name).ToList();
	var dict = AllCountries.ToDictionary(x => x.Code);
	this.AllCountriesByKey = dict;
	}
	}
	public class CsvReader
	{
	private string _csvFilePath;
	public CsvReader(string csvFilePath)
	{
	this._csvFilePath = csvFilePath;
	}
	public List<Country> ReadAllCountries()
	{
	List<Country> countries = new List<Country>();
	using (StreamReader sr = new StreamReader(_csvFilePath))
	{
	// read header line
	sr.ReadLine();
	string csvLine;
	while ((csvLine = sr.ReadLine()) != null)
	{
	countries.Add(ReadCountryFromCsvLine(csvLine));
	}
	}
	return countries;
	}
	public Country ReadCountryFromCsvLine(string csvLine)
	{
	string[] parts = csvLine.Split(',');
	string name;
	string code;
	string region;
	string popText;
	switch (parts.Length)
	{
	case 4:
	name = parts[0];
	code = parts[1];
	region = parts[2];
	popText = parts[3];
	break;
	case 5:
	name = parts[0] + ", " + parts[1];
	name = name.Replace("\"", null).Trim();
	code = parts[2];
	region = parts[3];
	popText = parts[4];
	break;
	default:
	throw new Exception($"Can't parse country from csvLine: {csvLine}");
	}
	// TryParse leaves population=0 if can't parse
	int.TryParse(popText, out int population);
	return new Country(name, code, region, population);
	}
	}
	/// <summary>
	/// Interaction logic for MainWindow.xaml
	/// </summary>
	public partial class MainWindow : Window
	{
	private AppData AllData { get; } = new AppData();
	public MainWindow()
	{
	InitializeComponent();
	}
	private void Window_Loaded(object sender, RoutedEventArgs e)
	{
	AllData.Initialize(@"F:\Advanced Collections\Code\PopByLargest.csv");
	this.DataContext = AllData;
	}
	private void tbxCountryCode_TextChanged(object sender, TextChangedEventArgs e)
	{
	string code = tbxCountryCode.Text;
	this.grdSelectCountry.DataContext = GetCountryWithCode(code);
	}
	private Country GetCountryWithCode(string code)
	{
	if (code.Length != 3)
	return null;
	AllData.AllCountriesByKey.TryGetValue(new CountryCode(code), out Country result);
	return result;
	}
	}
	public class Country
	{
	public string Name { get; }
	public CountryCode Code { get; }
	public string Region { get; }
	public int Population { get; }
	public Country(string name, string code, string region, int population)
	{
	this.Name = name;
	this.Code = new CountryCode(code);
	this.Region = region;
	this.Population = population;
	}
	public override string ToString() => $"{Name} ({Code})";
	}
	public class CountryCode
	{
	public string Value { get; }
	public CountryCode(string value)
	{
	Value = value;
	}
	public override string ToString() => Value;
	public override bool Equals(object obj)
	{
	if (obj is CountryCode other)
	return StringComparer.OrdinalIgnoreCase.Equals(this.Value, other.Value);
	return false;
	}
	public override int GetHashCode() =>
	StringComparer.OrdinalIgnoreCase.GetHashCode(this.Value);
	public static bool operator ==(CountryCode lhs, CountryCode rhs)
	{
	if (lhs != null)
	return lhs.Equals(rhs);
	else
	return rhs == null;
	}
	public static bool operator !=(CountryCode lhs, CountryCode rhs)
	{
	return !(lhs == rhs);
	}
	}

view raw dictionary.cs hosted with ❤ by GitHub

	Country Name	Country Code	Continent	Population 2017
	China	CHN	Asia	1386395000
	India	IND	Asia	1339180127
	United States	USA	North America	325719178
	Indonesia	IDN	Asia	263991379
	Brazil	BRA	South America	209288278
	Pakistan	PAK	Asia	197015955
	Nigeria	NGA	Africa	190886311
	Bangladesh	BGD	Asia	164669751
	Russian Federation	RUS	Europe	144495044
	Mexico	MEX	North America	129163276
	Japan	JPN	Asia	126785797
	Ethiopia	ETH	Africa	104957438
	Philippines	PHL	Asia	104918090
	Egypt, Arab Rep.	EGY	Africa	97553151
	Vietnam	VNM	Asia	95540800
	Germany	DEU	Europe	82695000
	Congo, Dem. Rep.	COD	Africa	81339988
	Iran, Islamic Rep.	IRN	Asia	81162788
	Turkey	TUR	Asia	80745020
	Thailand	THA	Asia	69037513
	France	FRA	Europe	67118648
	United Kingdom	GBR	Europe	66022273
	Italy	ITA	Europe	60551416
	Tanzania	TZA	Africa	57310019
	South Africa	ZAF	Africa	56717156
	Myanmar	MMR	Asia	53370609
	Korea, Rep.	KOR	Asia	51466201
	Kenya	KEN	Africa	49699862
	Colombia	COL	South America	49065615
	Spain	ESP	Europe	46572028
	Ukraine	UKR	Europe	44831159
	Argentina	ARG	South America	44271041
	Uganda	UGA	Africa	42862958
	Algeria	DZA	Africa	41318142
	Sudan	SDN	Africa	40533330
	Iraq	IRQ	Asia	38274618
	Poland	POL	Europe	37975841
	Canada	CAN	North America	36708083
	Morocco	MAR	Africa	35739580
	Afghanistan	AFG	Asia	35530081
	Saudi Arabia	SAU	Asia	32938213
	Uzbekistan	UZB	Asia	32387200
	Peru	PER	South America	32165485
	Venezuela, RB	VEN	South America	31977065
	Malaysia	MYS	Asia	31624264
	Angola	AGO	Africa	29784193
	Mozambique	MOZ	Africa	29668834
	Nepal	NPL	Asia	29304998
	Ghana	GHA	Africa	28833629
	Yemen, Rep.	YEM	Asia	28250420
	Madagascar	MDG	Africa	25570895
	Korea, Dem. People�s Rep.	PRK	Asia	25490965
	Australia	AUS	Oceania	24598933
	Cote d'Ivoire	CIV	Africa	24294750
	Cameroon	CMR	Africa	24053727
	Niger	NER	Africa	21477348
	Sri Lanka	LKA	Asia	21444000
	Romania	ROU	Europe	19586539
	Burkina Faso	BFA	Africa	19193382
	Malawi	MWI	Africa	18622104
	Mali	MLI	Africa	18541980
	Syrian Arab Republic	SYR	Asia	18269868
	Chile	CHL	South America	18054726
	Kazakhstan	KAZ	Asia	18037646
	Netherlands	NLD	Europe	17132854
	Zambia	ZMB	Africa	17094130
	Guatemala	GTM	North America	16913503
	Ecuador	ECU	South America	16624858
	Zimbabwe	ZWE	Africa	16529904
	Cambodia	KHM	Asia	16005373
	Senegal	SEN	Africa	15850567
	Chad	TCD	Africa	14899994
	Somalia	SOM	Africa	14742523
	Guinea	GIN	Africa	12717176
	South Sudan	SSD	Africa	12575714
	Rwanda	RWA	Africa	12208407
	Tunisia	TUN	Africa	11532127
	Cuba	CUB	North America	11484636
	Belgium	BEL	Europe	11372068
	Benin	BEN	Africa	11175692
	Bolivia	BOL	South America	11051600
	Haiti	HTI	North America	10981229
	Burundi	BDI	Africa	10864245
	Dominican Republic	DOM	North America	10766998
	Greece	GRC	Europe	10760421
	Czech Republic	CZE	Europe	10591323
	Portugal	PRT	Europe	10293718
	Sweden	SWE	Europe	10067744
	Azerbaijan	AZE	Asia	9862429
	Hungary	HUN	Europe	9781127
	Jordan	JOR	Asia	9702353
	Belarus	BLR	Europe	9507875
	United Arab Emirates	ARE	Asia	9400145
	Honduras	HND	North America	9265067
	Tajikistan	TJK	Asia	8921343
	Austria	AUT	Europe	8809212
	Israel	ISR	Asia	8712400
	Switzerland	CHE	Europe	8466017
	Papua New Guinea	PNG	Oceania	8251162
	Togo	TGO	Africa	7797694
	Sierra Leone	SLE	Africa	7557212
	Hong Kong SAR, China	HKG	Asia	7391700
	Bulgaria	BGR	Europe	7075991
	Serbia	SRB	Europe	7022268
	Lao PDR	LAO	Asia	6858160
	Paraguay	PRY	South America	6811297
	El Salvador	SLV	North America	6377853
	Libya	LBY	Africa	6374616
	Nicaragua	NIC	North America	6217581
	Kyrgyz Republic	KGZ	Asia	6201500
	Lebanon	LBN	Asia	6082357
	Denmark	DNK	Europe	5769603
	Turkmenistan	TKM	Asia	5758075
	Singapore	SGP	Asia	5612253
	Finland	FIN	Europe	5511303
	Slovak Republic	SVK	Europe	5439892
	Norway	NOR	Europe	5282223
	Congo, Rep.	COG	Africa	5260750
	Costa Rica	CRI	North America	4905769
	Ireland	IRL	Europe	4813608
	New Zealand	NZL	Oceania	4793900
	Liberia	LBR	Africa	4731906
	West Bank and Gaza	PSE	Asia	4684777
	Central African Republic	CAF	Africa	4659080
	Oman	OMN	Asia	4636262
	Mauritania	MRT	Africa	4420184
	Kuwait	KWT	Asia	4136528
	Croatia	HRV	Europe	4125700
	Panama	PAN	North America	4098587
	Georgia	GEO	Asia	3717100
	Moldova	MDA	Europe	3549750
	Bosnia and Herzegovina	BIH	Europe	3507017
	Uruguay	URY	South America	3456750
	Puerto Rico	PRI	North America	3337177
	Mongolia	MNG	Asia	3075647
	Armenia	ARM	Asia	2930450
	Jamaica	JAM	North America	2890299
	Albania	ALB	Europe	2873457
	Lithuania	LTU	Europe	2827721
	Qatar	QAT	Asia	2639211
	Namibia	NAM	Africa	2533794
	Botswana	BWA	Africa	2291661
	Lesotho	LSO	Africa	2233339
	Gambia, The	GMB	Africa	2100568
	Macedonia, FYR	MKD	Europe	2083160
	Slovenia	SVN	Europe	2066748
	Gabon	GAB	Africa	2025137
	Latvia	LVA	Europe	1940740
	Guinea-Bissau	GNB	Africa	1861283
	Kosovo	XKX	Europe	1830700
	Bahrain	BHR	Asia	1492584
	Trinidad and Tobago	TTO	North America	1369125
	Eswatini	SWZ	Africa	1367254
	Estonia	EST	Europe	1315480
	Timor-Leste	TLS	Asia	1296311
	Equatorial Guinea	GNQ	Africa	1267689
	Mauritius	MUS	Africa	1264613
	Cyprus	CYP	Asia	1179551
	Djibouti	DJI	Africa	956985
	Fiji	FJI	Oceania	905502
	Comoros	COM	Africa	813912
	Bhutan	BTN	Asia	807610
	Guyana	GUY	South America	777859
	Macao SAR, China	MAC	Asia	622567
	Montenegro	MNE	Europe	622471
	Solomon Islands	SLB	Oceania	611343
	Luxembourg	LUX	Europe	599449
	Suriname	SUR	South America	563402
	Cabo Verde	CPV	Africa	546388
	Malta	MLT	Europe	465292
	Maldives	MDV	Asia	436330
	Brunei Darussalam	BRN	Asia	428697
	Bahamas, The	BHS	North America	395361
	Belize	BLZ	North America	374681
	Iceland	ISL	Europe	341284
	Barbados	BRB	North America	285719
	French Polynesia	PYF	Oceania	283007
	New Caledonia	NCL	Oceania	280460
	Vanuatu	VUT	Oceania	276244
	Sao Tome and Principe	STP	Africa	204327
	Samoa	WSM	Oceania	196440
	St. Lucia	LCA	North America	178844
	Channel Islands	CHI	Europe	165314
	Guam	GUM	Oceania	164229
	Curacao	CUW	North America	161014
	Kiribati	KIR	Oceania	116398
	St. Vincent and the Grenadines	VCT	North America	109897
	Tonga	TON	Oceania	108020
	Grenada	GRD	North America	107825
	Virgin Islands (U.S.)	VIR	North America	107268
	Micronesia, Fed. Sts.	FSM	Oceania	105544
	Aruba	ABW	North America	105264
	Antigua and Barbuda	ATG	North America	102012
	Seychelles	SYC	Africa	95843
	Isle of Man	IMN	Europe	84287
	Andorra	AND	Europe	76965
	Dominica	DMA	North America	73925
	Bermuda	BMU	North America	65441
	Cayman Islands	CYM	North America	61559
	Greenland	GRL	North America	56171
	American Samoa	ASM	Oceania	55641
	St. Kitts and Nevis	KNA	North America	55345
	Northern Mariana Islands	MNP	Oceania	55144
	Marshall Islands	MHL	Oceania	53127
	Faroe Islands	FRO	Europe	49290
	Sint Maarten (Dutch part)	SXM	North America	41109
	Monaco	MCO	Europe	38695
	Liechtenstein	LIE	Europe	37922
	Turks and Caicos Islands	TCA	North America	35446
	Gibraltar	GIB	Europe	34571
	San Marino	SMR	Europe	33400
	St. Martin (French part)	MAF	North America	32125
	British Virgin Islands	VGB	North America	31196
	Palau	PLW	Oceania	21729
	Nauru	NRU	Oceania	13649
	Tuvalu	TUV	Oceania	11192
	Eritrea	ERI	Africa	..

view raw Population.csv hosted with ❤ by GitHub

 Note

The speed of retrieval depends on the quality of the hashing algorithm of the type specified for TKey.

Dictionary generic class provides a mapping from a set of keys to a set of values. Each addition to the dictionary consists of a value and its associated key. Retrieving a value by using its key is very fast, close to O(1), because the Dictionary class is implemented as a hash table.