To design this kind of report, you must specify a filter that filters out the required tasks; the data that should be displayed on the X and the Y axes; which parameter should represent the data; and which function should be calculated for the selected parameter. 

The X and the Y axes’ parameters can be any parameter having a fixed amount of values, including custom fields of the List type. The data can be any numeric field, including custom fields of the Integer and Double types. The following functions are available: max, min, avg, sum. Note that not every possible parameter combination can make sense. 

When constructing the report the system finds subtasks of the current task which satisfy the filter condition. After that the data is grouped based on parameters specified for the X and the Y axes, and for each group the value of the target function is calculated.

Let us assume you have chosen the following parameters:

X: Category
Y: Submitter
Value: Actual Budget
Function: Sum

In this scenario the system will determine the the worktime required to solve the task from the task submitter and the category of the task. The system will also calculate the total time expenses on each category, on each submitter and the total time spent on all the tasks. 

Let’s design a report demonstrating the distribution of the number of tasks depending on the category and the status:

X: category
Y: status
Value: Task Amount
Function: Sum

Create the calculated custom field 'submitdate' with the List type accounting the following formula:

Calendar ca = Calendar.getInstance();
ca.setTime(new Date(task.getSubmitdate().getTime()));
int day = ca.get(Calendar.DAY_OF_WEEK);
switch (day){
     case Calendar.SUNDAY: return "Sunday";
     case Calendar.MONDAY: return "Monday";
     case Calendar.TUESDAY: return "Tuesday";
     case Calendar.WEDNESDAY: return "Wednesday";
     case Calendar.THURSDAY: return "Thursday";
     case Calendar.FRIDAY: return "Friday";
     case Calendar.SATURDAY: return "Saturday";
}
return null;

The list of the possible values of the elements in the list must correspond to the list of possible results of the calculation of the formula. This calculated field returns the name of the day of the week when the task was created. 

In order to find out how many tasks are created and by whom on different days of the week, create the following filter:

X: submiday
Y: submitter
Value: Task Amount
Function: Sum

For Task Amount only the Sum function makes sense as the maximum and average value will be always equal to 1. Design the report in any format convenient for you. 

From this example of the report it is clear that the greatest amount of tasks are created by Max Kramarenko. It is also clear that the tasks are created predominantly on Fridays, and that the fewest amount of tasks are created on Thursdays.