CRM 2011 Chart: count of grouped dates for other field - charts

Question

I have an entity expressing employee absences split per half day (AM and PM). the entity has 4 relevant fields: the employee name (another custom entity), a reason for absence (holiday, overtime reimbursement, paid vacation, allowed leave,... 11 in total), the date of absence and whether it's an AM or PM absence (dropdown using 2 values). If an employee is absent the entire day, 2 records are made, 1 for AM and 1 for PM.
I now have to make a graph which shows the following:
Group all absences per employee (5 absent employees is 5 groups);
group all absences for a specific employee per reason for absence (an employee with 2 different absences gets 2 adjacent columns in his group);
The data shown is a count of all the absences, grouped by date (2 absences, 1 AM and 1 PM, on the same date should count as 1 absence, not 2). In effect, I need a count of unique dates.
I have managed to make a basic graph which has the employee and absence reason groups completed. However, I cannot figure out how to count unique dates.
What i've got so far is:
<visualization>
<visualizationid>{CA31385D-FE63-E311-A895-005056A03018}</visualizationid>
<name>Datum afwezigheid bij personeelsfiche en reden van afwezigheid</name>
<primaryentitytypecode>acm_tijdindeling</primaryentitytypecode>
<datadescription>
<datadefinition>
<fetchcollection>
<fetch mapping="logical" aggregate="true">
<entity name="acm_tijdindeling">
<attribute groupby="true" alias="group_personeelsfiche" name="acm_personeelsfiche" />
<attribute alias="count_datumafwezigheid" name="acm_datumafwezigheid" aggregate="count" />
<attribute groupby="true" alias="group_redenvanafwezigheid" name="acm_redenvanafwezigheid" />
</entity>
</fetch>
</fetchcollection>
<categorycollection>
<category alias="group_personeelsfiche">
<measurecollection>
<measure alias="count_datumafwezigheid" />
</measurecollection>
</category>
</categorycollection>
</datadefinition>
</datadescription>
<presentationdescription>
<Chart Palette="None" PaletteCustomColors="55,118,193; 197,56,52; 149,189,66; 117,82,160; 49,171,204; 255,136,35; 97,142,206; 209,98,96; 168,203,104; 142,116,178; 93,186,215; 255,155,83">
<Series>
<Series ChartType="Column" IsValueShownAsLabel="True" Font="{0}, 9.5px" LabelForeColor="59, 59, 59" CustomProperties="PointWidth=0.75, MaxPixelPointWidth=40"></Series>
</Series>
<ChartAreas>
<ChartArea BorderColor="White" BorderDashStyle="Solid">
<AxisY LabelAutoFitMinFontSize="8" TitleForeColor="59, 59, 59" TitleFont="{0}, 10.5px" LineColor="165, 172, 181" IntervalAutoMode="VariableCount">
<MajorGrid LineColor="239, 242, 246" />
<MajorTickMark LineColor="165, 172, 181" />
<LabelStyle Font="{0}, 10.5px" ForeColor="59, 59, 59" />
</AxisY>
<AxisX LabelAutoFitMinFontSize="8" TitleForeColor="59, 59, 59" TitleFont="{0}, 10.5px" LineColor="165, 172, 181" IntervalAutoMode="VariableCount">
<MajorTickMark LineColor="165, 172, 181" />
<MajorGrid LineColor="Transparent" />
<LabelStyle Font="{0}, 10.5px" ForeColor="59, 59, 59" />
</AxisX>
</ChartArea>
</ChartAreas>
<Titles>
<Title Alignment="TopLeft" DockingOffset="-3" Font="{0}, 13px" ForeColor="59, 59, 59"></Title>
</Titles>
<Legends>
<Legend Alignment="Center" LegendStyle="Table" Docking="right" IsEquallySpacedItems="True" Font="{0}, 11px" ShadowColor="0, 0, 0, 0" ForeColor="59, 59, 59" />
</Legends>
</Chart>
</presentationdescription>
<isdefault>false</isdefault>
</visualization>
I've tried adding groupby="true" dategrouping="day" to the count_datumafwezigheid aggregate, but then I get an "invalid XML" error.

Answer 1

Here's a link on how to count unique items http://crmchartguy.wordpress.com/2013/12/12/count-distinct-or-unique-items-in-ms-crm-charts/

Answer 2

I had a similar problem once - im not sure its possible to aggregate DateTime - See Thread:
Fetch DateTime CRM 2011