Power BI • choose your denominator — Define whether percent of total retains a region slicer or removes it, and expose the DAX filter modifications behind each denominator.

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<header><span class="eyebrow">Filter-context companion / fictional R1 model</span><h1>One count. Two different shares.</h1><p class="intro">Keep the current numerator; change which filters the denominator retains.</p></header>
<div class="toolbar"><div><span class="eyebrow">Region slicer</span><div class="controls"><button type="button" id="west" class="secondary">West</button><button type="button" id="east" class="secondary">East</button><button type="button" id="all" class="secondary">All regions</button></div></div><div><span class="eyebrow">Inspect visual context</span><div class="controls"><button type="button" id="cat-a" class="secondary">Category A</button><button type="button" id="cat-b" class="secondary">Category B</button><button type="button" id="subtotal" class="secondary">Subtotal</button></div></div></div>
<div class="grid results"><section class="result"><span class="eyebrow">Share of region</span><div class="big" id="region-share">75%</div><p id="region-trace">3 ÷ 4 = 0.75</p><div class="bar"><span id="region-bar" style="width:75%"></span></div><small>Remove category filter; retain selected region.</small></section><section class="result global"><span class="eyebrow">Share of all counts</span><div class="big" id="all-share">30%</div><p id="all-trace">3 ÷ 10 = 0.3</p><div class="bar"><span id="all-bar" style="width:30%"></span></div><small>Remove all denominator report-context filters.</small></section></div>
<p id="context" class="muted">West / Category A</p><p id="error" class="error" role="alert"></p>
<section class="panel"><h2>Matrix • numerator and both totals</h2><div class="table-wrap"><table><thead><tr><th>Row</th><th>Count</th><th>Region total</th><th>Region share</th><th>All total</th><th>All share</th></tr></thead><tbody id="matrix"></tbody></table></div><p id="bad-ratio" class="muted"></p></section>
<div class="grid"><section class="panel"><h2>Fixture counts</h2><p class="muted" id="revision">R1 • original counts</p><div class="grid"><div><label for="wa">West / A</label><input id="wa" type="number" value="3"><label for="wb">West / B</label><input id="wb" type="number" value="1"></div><div><label for="ea">East / A</label><input id="ea" type="number" value="2"><label for="eb">East / B</label><input id="eb" type="number" value="4"></div></div><div class="controls"><button type="button" id="apply">Apply revised counts</button><button type="button" id="zero" class="secondary">Separate zero fixture</button><button type="button" id="reset" class="secondary">Restore R1</button></div></section>
<section class="panel"><h2>Measures to review natively</h2><pre>Count = SUM(FactCounts[Count])
Region Total = CALCULATE([Count],
  REMOVEFILTERS(DimCategory[Category]))
Share of Region = DIVIDE([Count], [Region Total])
All Counts Total = CALCULATE([Count], REMOVEFILTERS())
Share of All Counts = DIVIDE([Count], [All Counts Total])</pre></section></div>
<details><summary>Model and filter manifest</summary><p>DimRegion contains unique West/East keys; DimCategory contains unique A/B keys. Active one-to-many, single-direction relationships filter FactCounts from each dimension. Visual rows use DimCategory[Category]; the slicer uses DimRegion[Region]. All keys match.</p><p>No other filters or security restrictions are in this fixture. Subtotals evaluate the measures without a category row filter; they do not average percentages. The separate all-zero fixture returns BLANK for zero denominators.</p></details>
<footer>JavaScript arithmetic illustrates the declared filter contract; this page does not run DAX, load a PBIX, or verify Power BI visuals. Native model and filter evidence is required. No security bypass or universal ALLSELECTED equivalence is implied. Values are fictional counts; edited data is not saved.</footer>
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let region='West',category='A',data=[3,1,2,4];
function shares(d,r,c){if(d.length!==4||d.some(x=>!Number.isFinite(x)||x<0))throw Error('Use four finite, nonnegative counts.');const selected=r==='West'?d.slice(0,2):r==='East'?d.slice(2):[d[0]+d[2],d[1]+d[3]];const denominator=selected[0]+selected[1],total=d.reduce((a,b)=>a+b,0),count=c==='Subtotal'?denominator:selected[c==='A'?0:1];if(!Number.isFinite(total))throw Error('Counts exceed the supported numeric range.');return {count,denominator,total,region:denominator===0?null:count/denominator,all:total===0?null:count/total}}
const percent=x=>x===null?'BLANK':Number((x*100).toFixed(4))+'%';
function render(){if(data===null)return;const s=shares(data,region,category);txt('region-share',percent(s.region));txt('all-share',percent(s.all));txt('region-trace',s.count+' ÷ '+s.denominator+' = '+(s.region===null?'Undefined: denominator is zero':s.region));txt('all-trace',s.count+' ÷ '+s.total+' = '+(s.all===null?'Undefined: denominator is zero':s.all));$('region-bar').style.width=(s.region===null?0:s.region*100)+'%';$('all-bar').style.width=(s.all===null?0:s.all*100)+'%';txt('context',region+' / '+(category==='Subtotal'?'Subtotal (no category-row filter)':'Category '+category));$('matrix').innerHTML=['A','B','Subtotal'].map(c=>{const x=shares(data,region,c);return '<tr'+(c===category?' class="active"':'')+'><th>'+c+'</th><td>'+x.count+'</td><td>'+x.denominator+'</td><td>'+percent(x.region)+'</td><td>'+x.total+'</td><td>'+percent(x.all)+'</td></tr>'}).join('');txt('bad-ratio',s.count?'Same-context counterexample: '+s.count+' ÷ '+s.count+' = 100%. This is not a share-of-total measure.':'Same-context counterexample: 0 ÷ 0 is BLANK, not 100%.');for(const [id,v]of [['west','West'],['east','East'],['all','All regions']])$(id).setAttribute('aria-pressed',String(region===v));for(const [id,v]of [['cat-a','A'],['cat-b','B'],['subtotal','Subtotal']])$(id).setAttribute('aria-pressed',String(category===v));txt('error','')}
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function apply(){try{const values=['wa','wb','ea','eb'].map(id=>{if(!$(id).value.trim())throw Error('Fill all four counts; blank is not zero.');return Number($(id).value)});shares(values,region,category);data=values;txt('revision',values.join(',')==='3,1,2,4'?'R1 • original counts':values.every(x=>x===0)?'Z0 • separate all-zero fixture':'Edited fixture • new expectations');render()}catch(e){invalidate();txt('error',e.message)}}
for(const [id,v]of [['west','West'],['east','East'],['all','All regions']])on(id,'click',()=>{region=v;render()});for(const [id,v]of [['cat-a','A'],['cat-b','B'],['subtotal','Subtotal']])on(id,'click',()=>{category=v;render()});for(const id of ['wa','wb','ea','eb']){on(id,'input',invalidate);enter(id,apply)}on('apply','click',apply);on('zero','click',()=>{for(const id of ['wa','wb','ea','eb'])$(id).value='0';apply()});on('reset','click',()=>{['wa','wb','ea','eb'].forEach((id,i)=>$(id).value=String([3,1,2,4][i]));region='West';category='A';apply()});render();
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