# Guide to Machine Learning in R for Beginners : Intro to Machine Learning

Quantitative variables typically have measurement units, such as pounds, dollars, years, volts, gallons, megabytes, inches, degrees, miles per hour, pounds per square inch, BTUs, and so on.Some variables, such as social security numbers and zip codes, take numerical values, but are not quantitative: They are qualitative or categorical variables..The sum of two zip codes or social security numbers is not meaningful..The average of a list of zip codes is not meaningful..Qualitative and categorical variables typically do not have units..Qualitative or categorical variables — such as gender, hair color, or ethnicity — group individuals..Qualitative and categorical variables have neither a “size” nor, typically, a natural ordering to their values..They answer questions such as “which kind?” The values categorical and qualitative variables take are typically adjectives (for example, green, female, or tall)..Arithmetic with qualitative variables usually does not make sense, even if the variables take numerical values..Categorical variables divide individuals into categories, such as gender, ethnicity, age group, or whether or not the individual finished high schoolLevels of Measurement:There are 4 levels of measurement: Nominal, Ordinal, Interval and Ratio.Ø A nominal measurement is one in which the values of the variable are names..The names of the different species of Galapagos tortoises are an example of a nominal measurement..These variables are categorical..Nominal variables are organized into non-numeric categories that cannot be ranked or compared quantitatively.. More details