Filters and First and Last Dates

I have a traditional project structure
A project has one or more Phases has one or more Tasks, each of these has a reference to the parent and each has a start and end date.

Project Name,                 Project Start, Project End
Phase Name,   Phase.Project,  Phase Start,   Phase End
Task Name,    Task.Phase,     Task Start     Task End

Rather than maintain multiple different date fields I’d rather use roll ups of start and end dates for the lower level record


Deliverable 1 has a start date of the earliest date of Tasks 1, 2 & 3.
Reading what I can find related to first and last dates I have tried multiple equations but keep coming up with blank rows. Could someone point me to an example please?

Many thanks.

Hey @Sean_Sloan a simple example would help. I think you could try something like list(task 1, task 2, task 3).startOrEndDate.min()

I hadn’t put an example because I didn’t want to show I didn’t have the remotest understanding of what I was trying to do, but… I think I have worked it out.

[Tasks].Filter([Tasks.Phase].Contains(thisRow)).Sort(true,[Tasks].[Due date - start]).first().[Due date - start]
and for end date
[Tasks].Filter([Tasks.Phase].Contains(thisRow)).Sort(true,[Tasks].[Due date - end]).last().[Due date - end]

That is to say it is showing what I expected - I have probably used a very expensive way to achieve it.