LibreOffice pivot table group by month

I'm not sure whether this was possible in LibreOffice that was current in the time when this question was asked but now this is quite easy to do, so if anyone stumbles upon this question this might help:

Using data from the input table (btw. for this last column "Month" is redundant) one should do the following.

Create Pivot table:

1. Select the table and from the menu select Data > Pivot Table > Create...
2. In the Column Fields is the Date field
3. In Row Fields is the Customer field
4. In Data Fields the Amount field

When the Pivot table is created:

1. Select/click on any cell in the row which contains dates
2. From the menu select Data > Group and Outline > Group
3. Select Group By > Intervals
4. Check Months (or any interval you would like)

I think the problem is that the "Month" column has different values for each date. So LibreOffice doesn't understand you want to group the output by distinct months.

Thus, a solution could be to "construct" a date based on cell A2, ignoring the day:

• Replace the Formula "=A2" in the "Month" column by

  =DATE(YEAR(A2),MONTH(A2),"1")

  This way, you will have the same date for every month cell, depending on the original date.

• Then, format that column using the pattern "MMMM" to display the date as "January".

• Now, refresh the Pivot Table or re-create it with "Month" in "Column Fields", "Customers" in "Row Fields" and "Sum - Amount" in "Data Fields".

This should yield the desired result.