QGIS 3.2 atlas with set of points

Just to add on to PieterB's answer here, you can create a virtual layer

'Layer'->'Add Layer'->'Add/Edit Virtual Layer'

Give it a query that will aggregate the geometries by 'att3'.

Then in the Layout set the coverage layer to this new Virtual Layer like so:

Make sure layout extents are controlled by Atlas.

edit:

You have to do 2 things:

• create a virtual_layer based on the unique values in "attr3" that will serve as coverage layer
• style your layer in that way so it shows only the features that are filtered in the printcomposer

1/ create coverage layer based on unique values: layer > add layer > add virtual layer

load your layer and as query add select distinct attr3 from your_layer_name

2/ set 'virtual layer' as coverage layer in the printcomposer and select "attr3" as Page name

3/ make a rule-based style "attr3"= @atlas_pagename

now activate the atlasfunction and you'll see only the filtered features