IMPORTING DATA INTO R. Import data from relational databases

Transcription

1 IMPORTING DATA INTO R Import data from relational databases

2 Up to now Single Files Flat files Excel files SPSS files

3 Relational Databases What is a relational database? How to connect? How to read table? Next Video: Database Queries

4 company Importing Data into R

5 company employees id name started_at 1 Tom Frank Julie Heather John

6 company employees id name started_at 1 Tom Frank Julie Heather John products id name contract 1 Easy Call 0 2 Call Plus 1 5 Small Biz 0 9 Biz Unlimited 1

7 company employees id name started_at 1 Tom Frank Julie Heather John products id name contract 1 Easy Call 0 2 Call Plus 1 sales id employee_id product_id date price Small Biz 0 9 Biz Unlimited 1

8 company employees id name started_at 1 Tom Frank Julie Heather John products id name contract 1 Easy Call 0 2 Call Plus 1 5 Small Biz 0 9 Biz Unlimited 1 relation sales id employee_id product_id date price relation

9 Database Management System DBMS Open source MySQL, PostgreSQL, SQLite Proprietary Oracle Database, Microsoft SQL Server SQL = Structured Query Language

10 Databases in R Different R packages MySQL RMySQL PostgresSQL RPostgresSQL Oracle Database ROracle Conventions specified in DBI > install.packages("rmysql") > library(dbi) # library(rmysql) not required

11 Connect to database Construct SQL driver > con <- dbconnect(rmysql::mysql(), dbname = "company", host = "courses.csrrinzqubik.us- east-1.rds.amazonaws.com", port = 3306, user = "student", password = "datacamp") con is DBIConnection object

12 List and import tables > dblisttables(con) [1] "employees" "products" "sales" > dbreadtable(con, "employees") employees id name started_at 1 Tom Frank Julie Heather John id name started_at 1 1 Tom Frank Julie Heather John > dbdisconnect(con) [1] TRUE > con Error in.local(dbobj,...) : internal error in RS_DBI_getConnection:...

13 IMPORTING DATA INTO R Let s practice!

14 IMPORTING DATA INTO R SQL Queries from inside R

15 Entire table dbreadtable() employees id name started_at 1 Tom Frank Julie Heather John Fraction of data? employees name started_at Julie John Selection

16 Selective importing SQL Queries DBI -> RMySQL, RPostgreSQL,... Just the basics of SQL

17 company employees id name started_at 1 Tom Frank Julie Heather John products id name contract 1 Easy Call 0 2 Call Plus 1 sales id employee_id product_id date price Small Biz 0 9 Biz Unlimited 1

18 company employees id name started_at 1 Tom Frank Julie Heather John Names of employees that started after ? sales id employee_id product_id date price products id name contract 1 Easy Call 0 2 Call Plus Small Biz 0 9 Biz Unlimited 1

19 Load package and connect > library(dbi) > con <- dbconnect(rmysql::mysql(), dbname = "company", host = "courses.csrrinzqubik.us- east-1.rds.amazonaws.com", port = 3306, user = "student", password = "datacamp")

20 Example 1 > employees <- dbreadtable(con, "employees") > subset(employees, subset = started_at > " ", select = name) name 3 Julie 4 Heather 5 John > dbgetquery(con, "SELECT name FROM employees WHERE started_at > \" \"") name 1 Julie 2 Heather 3 John

21 Example 1 > employees <- dbreadtable(con, "employees") > subset(employees, subset = started_at > " ", select = name) name 3 Julie 4 Heather 5 John subset dbreadtable() Entire table > dbgetquery(con, "SELECT name FROM employees WHERE started_at > \" \"") name 1 Julie 2 Heather Way more efficient for big databases! 3 John dbgetquery() SQL Fraction subset

22 company employees id name started_at 1 Tom Frank Julie Heather John products id name contract 1 Easy Call 0 2 Call Plus 1 sales id employee_id product_id date price Small Biz 0 9 Biz Unlimited 1

23 company employees id name started_at 1 Tom Frank Julie Heather John All variables of products with contract sales id employee_id product_id date price products id name contract 1 Easy Call 0 2 Call Plus Small Biz 0 9 Biz Unlimited 1

24 Example 2 > products <- dbreadtable(con, "products") > subset(products, subset = contract == 1) id name contract 2 2 Call Plus Biz Unlimited 1 keep all columns > dbgetquery(con, "SELECT * FROM products WHERE contract = 1") id name contract 1 2 Call Plus 1 single equals sign 2 9 Biz Unlimited 1

25 Example 2 > dbgetquery(con, "SELECT * FROM products WHERE contract = 1") id name contract 1 2 Call Plus Biz Unlimited 1

26 dbgetquery().por() -> read_por() > dbgetquery(con, "SELECT * FROM products WHERE contract = 1") id name contract 1 2 Call Plus Biz Unlimited 1.sav() -> read_sav() > res <- dbsendquery(con, "SELECT * FROM products WHERE contract = 1") > dbfetch(res) id name contract 1 2 Call Plus Biz Unlimited 1 > dbclearresult(res) [1] TRUE

27 dbfetch() one by one.por() -> read_por() > res <- dbsendquery(con, "SELECT * FROM products WHERE contract = 1").sav() -> read_sav() > while(!dbhascompleted(res)) { + chunk <- dbfetch(res, n = 1) + print(chunk) + } id name contract 1 2 Call Plus 1 id name contract 1 9 Biz Unlimited 1 [1] id name contract <0 rows> (or 0-length row.names) > dbclearresult(res) [1] TRUE

28 Disconnect > dbdisconnect(con) [1] TRUE

29 IMPORTING DATA INTO R Let s practice!