Excel - De-cumulate data in pivot table - excel

Question

Hope you'll be able to help me.
I have a table with 11 columns, the first one is a date, the next 9 ones are a way of uniquely identifying data and the 11th is a certain amount of money.
What I'm doing in a pivot table is showing the added amount according to one of the identifiers (lines) and dates (columns).
All is well and quite easy to do in a pivot table. Today though I was told that the amounts in my source table are actually cumulative since the beginning of the year.
What I mean is that there are recurring entries in that table and that if I have an entry with the 9 identifiers in january and the same in february and march for example, the value of the one in february is actually (february-january) and for march (march-february).
I could through the unique identifiers just add a column in my source table to identify and calculate the real amount, but I was wondering if there was a way to do so in the pivot table directly ?
Thanks !
Edit :
Here is a screenshot of a simplified version (only two identifiers)
In the fourth column is the amount I have, and in the fifth the real one, that I have to calculate, it is quite easy with only two columns as identifiers.
The goal here is that the pivot table at the bottom shows the "real" amount without me having to create a new column in my source table.
My example table

Answer 1

You can do it using Calculated Items. But it is cumbersome.
A Calculated Item is just another item that a Pivot Table field can take. It is defined in terms of the other items in the same field. For example, the field Date might have values of Jan17, Feb17, etc. A new calculated item called Difference can be added to the Date field and defined as =Feb17-Jan17. This new Difference item will appear whenever the Date field is used to provide row or column labels and the values displayed for it in the main body of the pivot table will be equal to the corresponding values for Feb17 less those for Jan17.
The discussion below is based (loosely) on the pivot table in the picture accompanying the question.
Calculated Items cannot be calculated on grouped fields, so it will be necessary to ungroup the Date field in the pivot table. This will cause the items in the field to be displayed in the same dd/mm/yyyy format as the source data. Changing these to the custom format of mmmyy makes them easier to work with. In English (rather than French) they get displayed as Jan17, Feb17, etc. using this format.
To add a new Calculated Item to the Date field, select any item in this field and locate the Calculated Item option via the ribbon. This has changed across versions of Excel, in Excel 2010 it is accessed via the "Fields, Items & Sets" button of the "Pivot Table Tools/Options" tab of the ribbon. In later versions it accessed via the "Calculations" button of the same tab. A dialog box will appear as illustrated below.
In the Name: box insert a suitable name such as Feb17Xand in the Formula: box enter =IF(Feb17=0,0,Feb17-Jan17). Click "Add" then "OK". The new Date item labelled Feb17X will appear in the pivot table and will show values of 20, 0 and 0 against projects A, B and C respectively.
Feb17X is the decumulated Date item for February. The IF is necessary because although the Amountvalues are cumulative, they only appear in the source data whenever a new Amount occurs in the month (for example Project B and Department IS has data showing for April and June but not for May).
Similar decumulated Date items can be defined in the same way for the other months.
For March, Mar17X is defined as
=IF(Mar17=0,0,Mar17-(Jan17+Feb17X))
and a new Mar17X item is added to the Date field. Unfortunately, this shows values of -28, 0 and 0 against projects A, B and C, respectively. To get the correct values displayed, it is necessary to add the Department field to the row labels in the pivot table (below the Project field) and then to use the "Collapse Entire Field" operation to stop the detail of the Department field from being visible.
The calculated items for the remaining months are added as expected - that for June is Jun17X and has formula
=IF(Jun17=0,0,Jun17-(Jan17+Feb17X+Mar17X+Apr17X+May17X))
Once the new items have been defined for the Date field, a filter is applied in the pivot table to remove the cumulative items ie, Feb17, Mar17, Apr17, May17 and Jun17. This results in the pivot table displaying the sum of the decumulated values as shown below.
A few points:
The zeroes in the pivot table can be suppressed from display by setting the number format of the Amount field to #
In the larger problem where each Amount is defined by a Date, Project and 8 further field values, the row labels of the pivot table will need to include Project and all 8 of the attribute fields. The latter 8 fields will need to be "collapsed out" of the display.
It is much, much simpler to add a decumulated Amount column to the
source data range rather than using the Calculated Item approach set
out here. Sorting the source data by the 9 attributes (Project
first then the remaining 8) and then by Date makes the task
of decumulation very easy. Simply compare the 9 attributes in a row
with the previous row: if the values are unchanged between the two
rows, subtract the previous row's Amount from the current row's,
otherwise leave the current row's Amount unchanged.