How to Create a Dot Chart on TI-Nspire
When working with categorical data, you have the option of creating a dot chart. In the first screen is a variation of a two-dice sum example. The first column (called first_die) uses the command =randint(1,6,50) to simulate rolling one die 50 times.
The second column (labeled second_die) represents the outcome of rolling a second die 50 times, and the third column (labeled total) represents the sum of the first two columns.
The second screen shows the result of pressing [MENU]→Data→Quick Graph. The current page layout is configured with a Data & Statistics page, and the default dot plot of the data contained in the Total column is graphed automatically.
How to change variables for a dot plot
Perhaps you want to view a dot plot depicting the distribution of the first_die data. To accomplish this task, follow these steps:
Move the cursor to the horizontal axis label at the bottom of the screen until the words Click or Enter to change variable appear.
Press [CLICK] to reveal a list of choices.
Use the Touchpad keys to highlight your choice and press [ENTER].
The third screen shows the result of changing the horizontal axis category from total to first_die. Notice that the scale on the horizontal axis changes automatically. You also have the option of changing this category to display the second_die data.
If you press [MENU]→Plot Properties, you see menu options to add or remove X and Y variables. These options enable you to switch back and forth between one- and two-variable data sets. They also allow you to switch your plots from a vertical orientation to a horizontal orientation and vice versa.
Consider, for example, the vertically oriented dot plot shown in the second screen. You can press [MENU]→Plot Properties→Remove X Variable to effectively remove the graph from the screen. Next, move the cursor to the left side of the screen until the words Click or Enter to add variable appear, press [CLICK], and select total from the list.
You see the same dot plot as before, but with a horizontal orientation. Alternatively, select total as the Y variable (instead of the X variable) and watch the orientation change.
How to change your window settings
The first screen shows the results of a two-dice sum experiment in which a sum of 2 and a sum of 12 never occurred. TI-Nspire, therefore, produces a horizontal scale that ranges from 3 to 11. To change these settings to range from 2 to 12, press [MENU]→Window/Zoom→Window Settings and change the XMin to 1.5 and XMax to 12.5.
Alternatively, you can grab ([CTRL][CLICK]) the tick marks and use the Touchpad to stretch or shrink the horizontal scale to make the desired adjustments. See the second screen.
In the third screen, the x-axis variable is switched back to first_die. Then [MENU]→Plot Properties→Force Categorical X is pressed, which treats each value in the list as categories, much as it would if this list contained words.
Forcing a categorical variable is a nice option that gives a clean-looking graph and is especially well-suited for a discrete variable such as the numerical value on a die. Switching to categorical data also gives the option of pressing [MENU]→Plot Type and selecting Bar Chart or Pie Chart.
When numerical data are switched to categorical data, TI-Nspire sorts by the first digit it sees. If you switched the dot plot for total from numerical to categorical, the values on the horizontal axis would go 10, 11, 12, 2, 3, . . . , 9 from left to right.
Fortunately, you can grab the labels and move the data columns so that the totals are in numeric order (or whatever order you wish).
Press [MENU]→Plot Properties→Force Numerical X to switch back to numeric values.