How to create this column?

[paulmak]

I need to create a calculated column named "25% percentile". I was told to use the two date fields, start_date and end_date, from the dataset. First of all I have to ignore those data rows if one of this date field is null. Then calculate the duration between the two date fields using "_date-between" function, then "rank" each of the data row (ignore the one with null date fields) then the total number of row multiply by 0.25 (25%) to get the exact rank number of the data row. If the number has decimal point after multiplying the 0.25, then round it up to the nearest integer, then display the "_date_between" of that data row to the cell.

I have to build several of these table with different percentile % (50, 75 and 90) and other such as Min, Max and median etc, the first one is using the start_date and end_date then the next table is using other date field and end_date. All the tables is created in a single report.

I need help to create this calculated column.

Thanks