Add calculations to summarize group data in Numbers for iCloud
For each group or subgroup in a categorized table, you can add a function (a predefined calculation, such as sum, count, or average) to summarize the data in a column. For example, in a table with shirt sales data categorized by month, you could add a function to count the number of shirts sold each month. You add these functions to the summary row, a special, unnumbered row that appears above each group.
Add a function to a summary row cell
You can add a summary row calculation to any group’s summary row. The same calculation is automatically added to all groups at the same level in the category’s hierarchy.
Click a cell in a summary row, then click the Summary Action button
and choose a function.A label row that shows the name of the function appears above the calculation. To hide the label row, see “Show or hide the label row” below.
Tip: To quickly sort the groups based on the summary cell values, select a summary cell, then Control-click (on a Mac) or right-click (on a Windows device) and choose a sort option.
Remove a function
Click the cell in the summary row with the function you want to remove, then click the Summary Action button
and choose Blank.
Show or hide the label row
The label row is an optional row that appears above the summary row; it shows the name of the category, and the name of any functions (count, subtotal, and so on). You can hide the label row to reduce the amount of information shown in a table.
Move the pointer over the empty square to the left of the group name (on the far-left end of a summary row), click the arrow that appears, then choose Hide Label Row or Show Label Row.
You can also chart the results of summary row calculations (for example, a chart that plots the number of shirts sold each month). Select the column with the summary calculations you want to chart, then click the Chart button 
in the toolbar.