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<head>
<link href="../favicon.ico" rel="shortcut icon" type="image/x-icon"/>
<link href="../style.css" rel="stylesheet"/>
<title>BQN: Search functions</title>
</head>
<div class="nav"><a href="https://github.com/mlochbaum/BQN">BQN</a> / <a href="../index.html">main</a> / <a href="index.html">doc</a></div>
<h1 id="search-functions">Search functions</h1>
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<p>The three search functions are Index of (<code><span class='Function'>⊐</span></code>), Progressive Index of (<code><span class='Function'>⊒</span></code>), and Member of (<code><span class='Function'>∊</span></code>). These are dyadic functions that search one argument ("searched-in") for major cells <a href="match.html">matching</a> cells from the other ("searched-for"). For example, Index of returns, for each cell in <code><span class='Value'>𝕩</span></code>, the index of the first cell in <code><span class='Value'>𝕨</span></code> that matches it.</p>
<table>
<thead>
<tr>
<th align="center"></th>
<th>Name</th>
<th align="center">for</th>
<th align="center">in</th>
<th>Return</th>
</tr>
</thead>
<tbody>
<tr>
<td align="center"><code><span class='Function'>⊐</span></code></td>
<td>Index of</td>
<td align="center"><code><span class='Value'>𝕩</span></code></td>
<td align="center"><code><span class='Value'>𝕨</span></code></td>
<td>Index of first match</td>
</tr>
<tr>
<td align="center"><code><span class='Function'>⊒</span></code></td>
<td>Progressive Index of</td>
<td align="center"><code><span class='Value'>𝕩</span></code></td>
<td align="center"><code><span class='Value'>𝕨</span></code></td>
<td>Index of first unused match</td>
</tr>
<tr>
<td align="center"><code><span class='Function'>∊</span></code></td>
<td>Member of</td>
<td align="center"><code><span class='Value'>𝕨</span></code></td>
<td align="center"><code><span class='Value'>𝕩</span></code></td>
<td><code><span class='Number'>1</span></code> if found, <code><span class='Number'>0</span></code> if not</td>
</tr>
<tr>
<td align="center"><code><span class='Function'>⍋⍒</span></code></td>
<td><a href="order.html#bins">Bins</a></td>
<td align="center"><code><span class='Value'>𝕩</span></code></td>
<td align="center"><code><span class='Value'>𝕨</span></code></td>
<td>Predecessor index</td>
</tr>
</tbody>
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<p>The searched-for argument is <code><span class='Value'>𝕩</span></code> in Index-of functions (<code><span class='Function'>⊐⊒</span></code>) and <code><span class='Value'>𝕨</span></code> in Member of (<code><span class='Function'>∊</span></code>). <a href="order.html#bins">Bins</a> Up and Down (<code><span class='Function'>⍋⍒</span></code>) are ordering functions but follow the same pattern as Index-of. It's split into cells, but not necessarily <em>major</em> cells: instead, the cells used match the rank of a major cell of the other (searched-in) argument. In the most common case, when the searched-in argument is a list, 0-cells are used for the search (we might also say elements, as it gives the same result).</p>
<p>The result is always an array containing one number for each searched-for cell. For Index of and Member of, every result is computed independently; for Progressive Index of the result for a cell can depend on earlier cells, in index order.</p>
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