MATLAB DATABASE TOOLBOX RELEASE NOTES User's Guide Page 429
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Analyze Large Data Sets in a Database with MapReduce
6-87
% intermKey is 'PartialCountSumDelay'
count = 0;
sum = 0;
while hasnext(intermValIter)
countSum = getnext(intermValIter);
count = count + countSum(1);
sum = sum + countSum(2);
end
meanDelay = sum/count;
% The key-value pair added to outKVStore will become the output of mapreduce
add(outKVStore,'MeanArrivalDelay',meanDelay);
Run MapReduce Using the Mapper and Reducer Functions
Run MapReduce with the DatabaseDatastore object dbds, mapper function
meanArrivalDelayMapper, and reducer function meanArrivalDelayReducer to
calculate the mean arrival delay in the flight data.
outds = mapreduce(dbds,@meanArrivalDelayMapper,@meanArrivalDelayReducer);
Display the Output from MapReduce
Read the table outtab from the output datastore outds using readall.
outtab = readall(outds)
outtab =
Key Value
______ ________
'MeanArrivalDelay' [7.12]
The table has only one row containing one key-value pair.
Display the mean arrival delay meanArrDelay from the table outtab.
meanArrDelay = outtab.Value{1}
meanArrDelay =
7.12
Close the DatabaseDatastore
Close the DatabaseDatastore, cursor, and database connection.
- Database Toolbox™ 1
- User's Guide 1
- How to Contact MathWorks 2
- Revision History 3
- Contents 5
- Working with Data Sources 11
- Using Database Explorer 12
- Using Visual Query Builder 12
- Functions — Alphabetical List 16
- Before You Begin 17
- 1 Before You Begin 18
- Working with Databases 19
- ) standard SQL 21
- Data Type Support 22
- Data Type Support 23
- Data Retrieval Restrictions 24
- Getting Started with Database 27
- Connection Options 32
- Connection Options 33
- Initial Setup Requirements 35
- Defining Database Drivers 36
- Interface” 38
- Oracle ODBC for Windows 70
- Administrator 71
- Oracle JDBC for Windows 74
- Oracle JDBC for Windows 75
- MySQL ODBC for Windows 83
- MySQL ODBC for Windows 85
- MySQL JDBC for Windows 89
- MySQL JDBC for Windows 91
- PostgreSQL ODBC for Windows 95
- PostgreSQL ODBC for Windows 97
- See Also 101
- More About 101
- PostgreSQL JDBC for Windows 102
- PostgreSQL JDBC for Windows 103
- SQLite JDBC for Windows 108
- SQLite JDBC for Windows 109
- Sybase ODBC for Windows 115
- Sybase ODBC for Windows 117
- Sybase JDBC for Windows 123
- Sybase JDBC for Windows 125
- Oracle JDBC for Mac OS X 144
- Oracle JDBC for Mac OS X 145
- Oracle JDBC for Linux 151
- Oracle JDBC for Linux 153
- MySQL JDBC for Mac OS X 158
- MySQL JDBC for Mac OS X 159
- MySQL JDBC for Linux 165
- MySQL JDBC for Linux 167
- PostgreSQL JDBC for Mac OS X 172
- PostgreSQL JDBC for Mac OS X 173
- PostgreSQL JDBC for Linux 179
- PostgreSQL JDBC for Linux 181
- SQLite JDBC for Mac OS X 186
- SQLite JDBC for Mac OS X 187
- SQLite JDBC for Linux 193
- SQLite JDBC for Linux 195
- Sybase JDBC for Mac OS X 200
- Sybase JDBC for Mac OS X 201
- Sybase JDBC for Linux 207
- Sybase JDBC for Linux 209
- ODBC-Compliant Databases 214
- JDBC-Compliant Databases 214
- Related Examples 216
- Connecting to a Database 217
- PostgreSQL 218
- Selecting Data 221
- Working with Large Data Sets 224
- About Driver Configurations 226
- Setting Up ODBC Data Sources 230
- Setting Up JDBC Data Sources 231
- 3 Working with Data Sources 232
- Removing JDBC Data Sources 234
- Fetching Data Common Errors 235
- OracleDataSource.makeURL 240
- Compatibility and Limitations 249
- 4 Using Database Explorer 252
- Configure Your Environment 256
- Work with Multiple Databases 267
- ODBC Drivers 269
- JDBC Drivers 269
- Generate SQL and MATLAB Code 275
- 5 Using Visual Query Builder 280
- Using Queries to Export Data 287
- Working with Preferences 293
- Working with Preferences 295
- How Do I Perform Batching? 299
- Displaying Query Results 301
- Displaying Query Results 303
- Charting Query Results 305
- Saving Queries in Files 339
- Editing Queries 341
- Create a Query Using a Date 350
- Create a Query Using a String 352
- Delete Data from Databases 358
- Bulk Insert into Oracle 368
- Bulk Insert into MySQL 372
- Close the connection 373
- Retrieve Image Data Types 374
- Retrieve Image Data Types 375
- Display Database Metadata 376
- Using Driver Functions 379
- About the exec Function 382
- Using Cursor Objects 382
- Working with Microsoft Excel 383
- Database Considerations 383
- About the fetch Function 390
- Database Consideration 393
- About Scrollable Cursors 400
- About the fastinsert Function 410
- Database Connection Objects 412
- Cursor Objects 413
- Driver Objects 414
- Database Metadata Objects 414
- Drivermanager Objects 415
- Resultset Objects 415
- Resultset Metadata Objects 415
- About the setdbprefs Function 417
- Allowable Properties 417
- Read the first five records 424
- Description 432
- Examples 432
- Input Arguments 434
- Output Arguments 435
- Alternatives 459
- 'ftab') 461
- Close the cursor object 469
- Import Numeric Data 469
- Name-Value Pair Arguments 479
- database 483
- Properties 517
- Object Functions 518
- Create Object 518
- Database Explorer 524
- Database Explorer 527
- 3 to import data starting 576
- importedkeys 591
- Compatibility 622
- Limitations 623
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