Follow-up Dax Drop Duplicates - powerbi

Question

Similiar to a question asked here,
Given, this table, I want to only keep the records where the email appears first.
email
firstname
Lastname
Address
City
Zip
ABC#XYZ.com
Scott
Johnson
A
Z
1111
ABC#XYZ.com
Bill
Johnson
B
Y
2222
ABC#XYZ.com
Ted
Smith
C
X
3333
DEF#QRP.com
Steve
Williams
D
W
4444
XYZ#LMN.com
Sam
Samford
E
U
5555
XYZ#LMN.com
David
Beals
F
V
6666
DEF#QRP.com
Stephen
Jackson
G
T
7777
TUV#DEF.com
Seven
Alberts
H
S
8888
<table border="1" class="dataframe">
<thead>
<tr style="text-align: right;">
<th>email</th>
<th>firstname</th>
<th>Lastname</th>
<th>Address</th>
<th>City</th>
<th>Zip</th>
</tr>
</thead>
<tbody>
<tr>
<td>ABC#XYZ.com</td>
<td>Scott</td>
<td>Johnson</td>
<td>A</td>
<td>Z</td>
<td>1111</td>
</tr>
<tr>
<td>ABC#XYZ.com</td>
<td>Bill</td>
<td>Johnson</td>
<td>B</td>
<td>Y</td>
<td>2222</td>
</tr>
<tr>
<td>ABC#XYZ.com</td>
<td>Ted</td>
<td>Smith</td>
<td>C</td>
<td>X</td>
<td>3333</td>
</tr>
<tr>
<td>DEF#QRP.com</td>
<td>Steve</td>
<td>Williams</td>
<td>D</td>
<td>W</td>
<td>4444</td>
</tr>
<tr>
<td>XYZ#LMN.com</td>
<td>Sam</td>
<td>Samford</td>
<td>E</td>
<td>U</td>
<td>5555</td>
</tr>
<tr>
<td>XYZ#LMN.com</td>
<td>David</td>
<td>Beals</td>
<td>F</td>
<td>V</td>
<td>6666</td>
</tr>
<tr>
<td>DEF#QRP.com</td>
<td>Stephen</td>
<td>Jackson</td>
<td>G</td>
<td>T</td>
<td>7777</td>
</tr>
<tr>
<td>TUV#DEF.com</td>
<td>Seven</td>
<td>Alberts</td>
<td>H</td>
<td>S</td>
<td>8888</td>
</tr>
</tbody>
</table>
Expected output table:
email
firstname
Lastname
Address
City
Zip
ABC#XYZ.com
Scott
Johnson
A
Z
1111
DEF#QRP.com
Steve
Williams
D
W
4444
XYZ#LMN.com
Sam
Samford
E
U
5555
TUV#DEF.com
Seven
Alberts
H
S
8888
<table border="1" class="dataframe">
<thead>
<tr style="text-align: right;">
<th>email</th>
<th>firstname</th>
<th>Lastname</th>
<th>Address</th>
<th>City</th>
<th>Zip</th>
</tr>
</thead>
<tbody>
<tr>
<td>ABC#XYZ.com</td>
<td>Scott</td>
<td>Johnson</td>
<td>A</td>
<td>Z</td>
<td>1111</td>
</tr>
<tr>
<td>DEF#QRP.com</td>
<td>Steve</td>
<td>Williams</td>
<td>D</td>
<td>W</td>
<td>4444</td>
</tr>
<tr>
<td>XYZ#LMN.com</td>
<td>Sam</td>
<td>Samford</td>
<td>E</td>
<td>U</td>
<td>5555</td>
</tr>
<tr>
<td>TUV#DEF.com</td>
<td>Seven</td>
<td>Alberts</td>
<td>H</td>
<td>S</td>
<td>8888</td>
</tr>
</tbody>
</table>

Answer 1

There is no inherent ordering of a table in DAX, so in order to take the first row you need to add an index column or define an ordering on the table somehow.
For this answer, I'll assume that you've added an index column somehow (in the query editor or with a DAX calculated column).
You can create a filtered table as follows:
FilteredTable1 =
FILTER (
Table1,
Table1[Index]
= CALCULATE ( MIN ( Table1[Index] ), ALLEXCEPT ( Table1, Table1[email] ) )
)
For each row in Table1, this checks if the index is minimal over all the rows with the same email.

Answer 2

Assuming that we added an Index column with non duplicate values, it's possible to reduce the number of context transitions to only one per Email by preparing an Indexes table containing the indexes to be selected, and then apply this Indexes table as a filter using TREATAS.
T Index Unique =
VAR Indexes =
SELECTCOLUMNS(
ALL( 'T Index'[Email] ),
"MinIndex", CALCULATE( MIN( 'T Index'[Index] ) )
)
RETURN
CALCULATETABLE( 'T Index', TREATAS( Indexes, 'T Index'[Index] ) )
If instead we have non-unique column across the different Emails but unique per each email, like a timestamp, we can prepare a filter table containing the email and the timestamp
For instance with a T Date table like the following
The calculated table becomes
T Date Unique =
VAR EmailDate =
ADDCOLUMNS(
ALL( 'T Date'[Email] ),
"MinDate", CALCULATE( MIN( 'T Date'[Date] ) )
)
RETURN
CALCULATETABLE( 'T Date', TREATAS( EmailDate, 'T Date'[Email], 'T Date'[Date] ) )