Download the customer data and read into R.
customer <- read.csv(file = "https://xiaoruizhu.github.io/Data-Mining-R/lecture/data/CustomerData.csv")
- How many rows and columns of the dataset?
 - Print first few rows the dataset.
 - Obtain the summary statistics (Min, Median, Max, Mean and Std.) for Age, EducationYears, HHIncome, and CreditDebt.
 - Obtain the mean of HHIncome by MaritalStatus
 - Obtain a pivot table of LoanDefault vs. JobCategory. Which Job Category has the highest and lowerst loan default rate?
 
- Obtain a dataset “iris_select” that drop the first and second column by using dataname[, “variable_index”];
 - Create new variable Sepal_LW equals to the ratio of sepal length to sepal width. (without using mutate());
 - How to get only those variables that contain missing values?
 - Random sample a training data set that contains 80% of original data points.