**R-exercises**, and kindly contributed to R-bloggers)

The `ftable()`

function combines Cross-Tabulation with the ability to format , or “flatten”, contingency tables of 3 or more dimensions.

The resulting tables contain the combined counts of the categorical variables, (also factor variables in R), that are then arranged as a matrix, whose rows and columns correspond to the original data’s rows and columns. The `ftable()`

parameters, `row.vars`

and `col.vars`

, control the format of the table.

Displaying a contingency table in this flat matrix form is often preferable to showing it as a higher-dimensional array. The `write.ftable`

, and `read.ftable`

, functions allow for the saving, and accessing of Contigency Tables of 3 or more dimensions.

Answers to the exercises are available here.

**Exercise 1**

In order to demonstrate the `ftable()`

function’s capabilities, input the `Titanic`

data from R:

`data(Titanic)`

For the first exercise, create a basic flat contingency table from the Titanic data, using the `ftable()`

function.

**Exercise 2**

The `row.vars`

argument specifies the table variables that will format as table rows. `row.vars=`

is definable with variable numbers, or the variable names.

Therefore, use `row.vars`

= to specify the variable, `Class`

, as the row variables.

**Exercise 3**

Combine the `row.vars`

and `col.vars`

arguments to specify `Class`

& `Sex`

as the row variables, and `Survived`

as the column variable.

`row.vars`

and `col.vars`

are definable with variable numbers, or the variable names.

**Exercise 4**

With the parameters from the ftable used in Exercise 3, reverse the order of the `Class`

and `Sex`

columns.

**Exercise 5**

Next, using the `ftable()`

code from Exercise 4, specify `Age`

as the column variable.

As you can see from this exercise, `ftable()`

allows for the formatting of data for different areas of inquiry.

**Exercise 6**

Using the `data.frame()`

function will coerce ftable columns into rows. To demonstrate this, place the `ftable()`

from Exercise 5, within the `data.frame()`

function.

**Exercise 7**

Function `ftable.formula`

provides a formula interface, (a data = . argument), for creating flat contingency tables.

For example:

`ftable(Survived ~ ., data = Titanic)`

Use the formula interface for `ftable()`

to display the quantities in the `Titanic`

data for Male/Female passengers, by `Class`

and `Age`

.

**Exercise 8**

The `ftable()`

function creates an object of class `ftable`

. In order to demonstrate this, save the results of the ftable formula from Exercise 5 as an ftable variable called `titanicStats`

.

**Exercise 9**

Using the `write.table()`

function, write the ftable, `titanicStats`

, to a file. Make sure your working directory is set to a folder where you can find the resulting file. Name the file, “table1”.

**Exercise 10**

`read.ftable()`

reads in a flat-like contingency table from a file.

Using `read.ftable()`

, read the file, “table1”, into an R language environment variable called `data1`

.

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