Tag: Select (SQL)

Google Refine

An interesting data cleaning software from Google at

https://code.google.com/p/google-refine/

From the page at

https://code.google.com/p/google-refine/wiki/UserGuide

The Basics

First, although Google Refine might start out looking like a spreadsheet program (Microsoft Excel, Google Spreadsheets, etc.), don’t expect it to work like a spreadsheet program. That’s almost like expecting a database to work like a text editor.

Google Refine is NOT for entering new data one cell at a time. It is NOT for doing accounting.

Google Refine is for applying transformations over many existing cells in bulk, for the purpose of cleaning up the data, extending it with more data from other sources, and getting it to some form that other tools can consume.

To use Google Refine, think in big patterns. For example, to spot errors, think

  • Show me every row where the string length of the customer’s name is longer than 50 characters (because I suspect that the customer’s address is mistakenly included in the name field)
  • Show me every row where the contract fee is less than 1 (because I suspect the fee was entered in unit of thousand dollars rather than dollars)
  • Show me every row where the description field (scraped from some web site) contains “&” (because I suspect it wasn’t decoded properly)

To edit data, think

  • For every row where the contract fee is less than 1, multiply the fee by 1000.
  • For every row where the customer name contains a comma (it has been entered as “last_name, first_name”), split the name by the comma, reverse the array, and join it back with a space (producing “first_name last_name”)

To specify patterns, use filters and facets. Typically, you create a filter or facet on a particular column. For example, you can create a numeric facet on the “contract fee” column and adjust its range selector to select values less than 1. If the default facet doesn’t do what you want, you can configure it (by clicking “change” on the facet’s header). For example, you can create a text facet with on the same “contract fee” column with this expression:

  value < 1

It will show 2 choices: true and false. Just select true. Then, invoke the Transform command on that same column and enter the expression

  value * 1000

That Transform command affects only rows where the “contract fee” cell contains a value less than 1.

You can use several filters and facets together. Only rows that are selected by all facets and filters will be shown in the data table. For example, say you have two text facets, one on the “contract fee” column with the expression

  value < 1

and another on the “state” column (with the default expression). If you select “true” in the first facet and “Nevada” in the second, then you will only see rows for contracts in Nevada with fees less than 1.

Analogies

Databases

If you have programmed databases before (performing SQL queries), then what Google Refine works should be quite familiar to you. Creating filters and facets and selecting something in them is like performing this SELECT statement:

  SELECT *
  WHERE ... constraints determined by selection in facets and filters ...

And invoking the Transform command on a column while having some filters and facets selected is like performing this UPDATE statement

  UPDATE whole_table SET column_X = ... expression ...
  WHERE ... constraints determined by selection in facets and filters ...

The difference between Google Refine and databases is that the facets show you choices that you can select, whereas databases assume that you already know what’s in the data.

 

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Using PostgreSQL and MySQL databases in R 2.12 for Windows

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If you use Windows for your stats computing and your data is in a database (probably true for almost all corporate business analysts) R 2.12 has provided a unique procedural hitch for you NO BINARIES for packages used till now to read from these databases.

The Readme notes of the release say-

Packages related to many database system must be linked to the exact
version of the database system the user has installed, hence it does
not make sense to provide binaries for packages
	RMySQL, ROracle, ROracleUI, RPostgreSQL
although it is possible to install such packages from sources by
	install.packages('packagename', type='source')
after reading the manual 'R Installation and Administration'.

So how to connect to Databases if the Windows Binary is not available-

So how to connect to PostgreSQL and MySQL databases.

For Postgres databases-

You can update your PostgreSQL databases here-

http://www.postgresql.org/download/windows

Fortunately the RpgSQL package is still available for PostgreSQL

  • Using the RpgSQL package

library(RpgSQL)

#creating a connection
con <- dbConnect(pgSQL(), user = "postgres", password = "XXXX",dbname="postgres")

#writing a table from a R Dataset
dbWriteTable(con, "BOD", BOD)

# table names are lower cased unless double quoted. Here we write a Select SQL query
dbGetQuery(con, 'select * from "BOD"')

#disconnecting the connection
dbDisconnect(con)

You can also use RODBC package for connecting to your PostgreSQL database but you need to configure your ODBC connections in

Windows Start Panel-

Settings-Control Panel-

Administrative Tools-Data Sources (ODBC)

You should probably see something like this screenshot.

Coming back to R and noting the name of my PostgreSQL DSN from above screenshot-( If not there just click on add-scroll to appropriate database -here PostgreSQL and click on Finish- add in the default values for your database or your own created database values-see screenshot for help with other configuring- and remember to click Test below to check if username and password are working, port is correct etc.

so once the DSN is probably setup in the ODBC (frightening terminology is part of databases)- you can go to R to connect using RODBC package


#loading RODBC

library(RODBC)

#creating a Database connection
# for username,password,database name and DSN name

chan=odbcConnect("PostgreSQL35W","postgres;Password=X;Database=postgres")

#to list all table names

sqlTables(chan)


TABLE_QUALIFIER TABLE_OWNER TABLE_NAME TABLE_TYPE REMARKS
1       postgres      public        bod      TABLE      
 2        postgres      public  database1      TABLE      
 3        postgres      public         tt      TABLE

Now for MySQL databases it is exactly the same code except we download and install the ODBC driver from http://www.mysql.com/downloads/connector/odbc/

and then we run the same configuring DSN as we did for postgreSQL.

After that we use RODBC in pretty much the same way except changing for the default username and password for MySQL and changing the DSN name for the previous step.

channel <- odbcConnect("mysql","jasperdb;Password=XXX;Database=Test")
test2=sqlQuery(channel,"select * from jiuser")
test2
 id  username tenantId   fullname emailAddress  password externallyDefined enabled previousPasswordChangeTime1  1   jasperadmin        1 Jasper Administrator           NA 349AFAADD5C5A2BD477309618DC              NA    01                       
2  2       joe1ser        1             Joe User           NA                 4DD8128D07A               NA    01
odbcClose(channel)
While using RODBC for all databases is a welcome step, perhaps the change release notes for Window Users of R may need to be more substantiative than one given for R 2.12.2
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