How is remove duplicate actually work?

Ok, remove duplicates. Powerful and scary at the same time. I've killed myself over it in years past, not just in DOMO. I'm happy to share what I've learned. Hope it helps.

Here is our pretend data:

Shape     Weight    Color    Date
Square    3         blue     2019-01-01
Square    3         blue     2019-02-01
Square    3         blue     2019-07-01
Square    23        blue     2019-05-01
Square    23        blue     2019-04-01
Square    3         red      2019-03-01
Circle    4         green    2019-01-01
Circle    4         green    2019-11-01
Circle    4         green    2019-03-01
Circle    10        orange   2019-07-01

If I use [Remove Dulicates] and key only on the `Shape` field I will only get two rows. The simple, frustrating, hard truth is that I CANNOT control which two rows. The only thing I know for sure is that both "Square" and "Circle" will be represented. Here are some thoughts on this:

Both this...
Square    3         blue     2019-01-01
Circle    4         green    2019-01-01

And this are equally possible:
Circle    10        orange   2019-07-01
Square    23        blue     2019-05-01

This is NOT possible because 
   - red and 23 are never on the same row
   - orange and 4 are never on the same row
Square    23        red      2019-04-01
Circle    4         orange   2019-07-01

[Remove Duplicates] will not 'mix and match' values from various columns. It will pick one row and use that row. 

The Real Question

I'm guessing the real question is, "How do I control which line is kept?"

This is possible. I would recommend that you use the [Rank & Window] action. If you are dealing with appended data or otherwise just want the record with the 'max date' or similar concept then also consider this article: Only using data from latest append

Rank & Window

Your first time trying to follow the setup screen for [Rank & Window] will likely be tricky, but it is not a difficult process. Honestly, filling out the boxes in Domo will be the hardest part and I think people quit there because they're not really sure it'll work anyways and when it doesn't run right they don't realize it was just a mix-match in the setup.

Before you go down this path you must ask if there is a way to identify which record you want by sorting on one or more columns. If the data is so ambiguous that you cannot create logic to single out the record you want then it won't be possible for Domo to get there either.

In our case we want the heaviest weight, and earliest date. We will use [Rank & Window] to sort the records that way and then add a `Row Number` based on that order. So 1 is the heaviest that is earliest date, and on down.

For Step 1 in the [Rank and Window Action] click "Add Function" which presents you with a new screen with it's own step 1 and 2:

1. Name the field `Row Number` or something obvious like that.
2. Pick 'Row Number' from the list.
3. Click "Apply" in the upper right corner (you might have to scroll up). This step alone gets people lost an unable to continue.

Now, those were substeps of step 1, now we move on to the real step 2 and 3: 

We will add two sets here, each with a column and sort order. The first column is `Weight` and the sort order is Descending. The second set is for column `Date` and is sorted Ascending.

Step 4 is our grouping. What field do we want to group by, in our case it is `Shape`.

Now we can preview and the data will look like this:

Shape     Weight    Color    Date         Row Number
Square    3         blue     2019-01-01   3
Square    3         blue     2019-02-01   4
Square    3         blue     2019-07-01   6
Square    23        blue     2019-05-01   2
Square    23        blue     2019-04-01   1
Square    3         red      2019-03-01   5
Circle    4         green    2019-01-01   2
Circle    4         green    2019-11-01   4
Circle    4         green    2019-03-01   3
Circle    10        orange   2019-07-01   1

By playing with various setup choices for the field and sort order in steps 2 & 3 we can change that row number order until we like what we have.

Regardless of the order, I can now [Filter Rows] and filter to `Row Number` = 1 and my final data looks like: 

Shape     Weight    Color    Date         Row Number
Square    23        blue     2019-04-01   1
Circle    10        orange   2019-07-01   1

Hope this helps!!