Example 1: Analyzing Car Performance with mtcars Dataset

Let’s start with the mtcars dataset, which contains information about various car models. Suppose we want to understand the distribution of cars based on the number of cylinders and the transmission type. We can use xtabs() to accomplish this:

# Create a contingency table using xtabs()
table_cars <- xtabs(~ cyl + am, data = mtcars)

# View the resulting table
table_cars

   am
cyl  0  1
  4  3  8
  6  4  3
  8 12  2

In this example, the formula ~ cyl + am specifies that we want to cross-tabulate the “cyl” (number of cylinders) variable with the “am” (transmission type) variable. The resulting table provides a clear breakdown of car counts based on these two factors.

The xtabs() function also allows you to specify the order of the variables in the formula. For example, the following formula would create the same contingency table as the previous formula, but the rows of the table would be ordered by the number of cylinders in the car:

xtabs(~am + cyl, data = mtcars)

   cyl
am   4  6  8
  0  3  4 12
  1  8  3  2

Example 2: Analyzing Health Data with healthyR.data

Let’s now explore the healthyR.data::healthyR_data dataset, which is a simulated administrative dataset. Suppose we’re interested in analyzing the distribution of patients’ insurance type based on their type of stay. Here’s how we can use xtabs() for this analysis:

# Load the dataset
library(healthyR.data)

# Create a contingency table using xtabs()
table_health <- xtabs(~ payer_grouping + ip_op_flag, data = healthyR_data)

# View the resulting table
table_health

                ip_op_flag
payer_grouping       I     O
  ?                  1     0
  Blue Cross     10797 13560
  Commercial      3328  3239
  Compensation     787  1715
  Exchange Plans  1206  1194
  HMO             8113  9331
  Medicaid        7131  1646
  Medicaid HMO   15466 10018
  Medicare A     52621     1
  Medicare B       293 22270
  Medicare HMO   13572  5425
  No Fault        1713   645
  Self Pay        2089  1560

In this example, the formula ~ payer_grouping + ip_op_flag specifies that we want to cross-tabulate the “payer_grouping” variable with the “ip_op_flag” variable. By using xtabs(), we obtain a comprehensive summary of patients’ insurance type and their stay type.