Lecture Notes

Lecture Notes: Information Processing in R

The R Programming Language

The R programming language is one of the most commonly used languages for ad hoc data analysis in business when Excel is not sufficient or not able to handle large data sets.

Programming with R

Environments:

R Console
R Studio with R Notebooks

Variables & Identifiers:

Variables hold values: scalars, text strings, data frames, results from calls to functions
Variables have names that must follow certain rules: must start with a letter, can contain letters digits and certain special characters including dot (.) and underscore (_).
Legal Variable Names:
- df
- df2
- df.txns
- df_all2017
Illegal Variable Names:
- 2df -- cannot start with a digit
- rs$all -- cannot contain a $; the $ is used to access columns in a dataframe
- rs# -- only . and _ are allowed in addition to digits and letters

Data & Object Types:

Variables are typed in R based on what value they contain:
The types can change simply by assigning a new value
Types can be converted using as.xxxx functions, e.g., as.numeric or as.date or as.string
Conversions are often necessary when data is read from CSV or XML files or databases

Data Frames

Data frames are essentially spreadsheets; they are tables of rows and columns where each row is a data case and each column is a value.

Loading Data from Files

Data Sets for code below:

Salaries.csv

Queries on Data Frames

Loading Data from Database into Data Frame with SQL

Data Sets & SQLite database for code below:

Salaries.csv | ProjectDB.db

Loading XML File into R

requires the library XML, so after installing the library from CRAN, use the command library(XML)