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<div class="section" id="record-io-pack-free-format-data-in-binary-files">
<span id="record-io-pack-free-format-data-in-binary-files"></span><h1>Record IO - Pack free-format data in binary files<a class="headerlink" href="#record-io-pack-free-format-data-in-binary-files" title="Permalink to this headline"></a></h1>
<p>This tutorial will walk through the python interface for reading and writing
record io files. It can be useful when you need more more control over the
details of data pipeline. For example, when you need to augment image and label
together for detection and segmentation, or when you need a custom data iterator
for triplet sampling and negative sampling.</p>
<p>Setup environment first:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="o">%</span><span class="n">matplotlib</span> <span class="n">inline</span>
<span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">print_function</span>
<span class="kn">import</span> <span class="nn">mxnet</span> <span class="kn">as</span> <span class="nn">mx</span>
<span class="kn">import</span> <span class="nn">numpy</span> <span class="kn">as</span> <span class="nn">np</span>
<span class="kn">import</span> <span class="nn">matplotlib.pyplot</span> <span class="kn">as</span> <span class="nn">plt</span>
</pre></div>
</div>
<p>The relevant code is under <code class="docutils literal"><span class="pre">mx.recordio</span></code>. There are two classes: <code class="docutils literal"><span class="pre">MXRecordIO</span></code>,
which supports sequential read and write, and <code class="docutils literal"><span class="pre">MXIndexedRecordIO</span></code>, which
supports random read and sequential write.</p>
<div class="section" id="mxrecordio">
<span id="mxrecordio"></span><h2>MXRecordIO<a class="headerlink" href="#mxrecordio" title="Permalink to this headline"></a></h2>
<p>First let’s take a look at <code class="docutils literal"><span class="pre">MXRecordIO</span></code>. We open a file <code class="docutils literal"><span class="pre">tmp.rec</span></code> and write 5
strings to it:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">record</span> <span class="o">=</span> <span class="n">mx</span><span class="o">.</span><span class="n">recordio</span><span class="o">.</span><span class="n">MXRecordIO</span><span class="p">(</span><span class="s1">'tmp.rec'</span><span class="p">,</span> <span class="s1">'w'</span><span class="p">)</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">5</span><span class="p">):</span>
<span class="n">record</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s1">'record_</span><span class="si">%d</span><span class="s1">'</span><span class="o">%</span><span class="n">i</span><span class="p">)</span>
<span class="n">record</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<p>Then we can read it back by opening the same file with ‘r’:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">record</span> <span class="o">=</span> <span class="n">mx</span><span class="o">.</span><span class="n">recordio</span><span class="o">.</span><span class="n">MXRecordIO</span><span class="p">(</span><span class="s1">'tmp.rec'</span><span class="p">,</span> <span class="s1">'r'</span><span class="p">)</span>
<span class="k">while</span> <span class="bp">True</span><span class="p">:</span>
<span class="n">item</span> <span class="o">=</span> <span class="n">record</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">item</span><span class="p">:</span>
<span class="k">break</span>
<span class="k">print</span> <span class="n">item</span>
<span class="n">record</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
</div>
<div class="section" id="mxindexedrecordio">
<span id="mxindexedrecordio"></span><h2>MXIndexedRecordIO<a class="headerlink" href="#mxindexedrecordio" title="Permalink to this headline"></a></h2>
<p>Some times you need random access for more complex tasks. <code class="docutils literal"><span class="pre">MXIndexedRecordIO</span></code> is
designed for this. Here we create a indexed record <code class="docutils literal"><span class="pre">tmp.rec</span></code> and a corresponding
index file <code class="docutils literal"><span class="pre">tmp.idx</span></code>:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">record</span> <span class="o">=</span> <span class="n">mx</span><span class="o">.</span><span class="n">recordio</span><span class="o">.</span><span class="n">MXIndexedRecordIO</span><span class="p">(</span><span class="s1">'tmp.idx'</span><span class="p">,</span> <span class="s1">'tmp.rec'</span><span class="p">,</span> <span class="s1">'w'</span><span class="p">)</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">5</span><span class="p">):</span>
<span class="n">record</span><span class="o">.</span><span class="n">write_idx</span><span class="p">(</span><span class="n">i</span><span class="p">,</span> <span class="s1">'record_</span><span class="si">%d</span><span class="s1">'</span><span class="o">%</span><span class="n">i</span><span class="p">)</span>
<span class="n">record</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<p>We can then access records with keys:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">record</span> <span class="o">=</span> <span class="n">mx</span><span class="o">.</span><span class="n">recordio</span><span class="o">.</span><span class="n">MXIndexedRecordIO</span><span class="p">(</span><span class="s1">'tmp.idx'</span><span class="p">,</span> <span class="s1">'tmp.rec'</span><span class="p">,</span> <span class="s1">'r'</span><span class="p">)</span>
<span class="n">record</span><span class="o">.</span><span class="n">read_idx</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
</pre></div>
</div>
<p>You can list all keys with:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">record</span><span class="o">.</span><span class="n">keys</span>
</pre></div>
</div>
</div>
<div class="section" id="packing-and-unpacking-data">
<span id="packing-and-unpacking-data"></span><h2>Packing and Unpacking Data<a class="headerlink" href="#packing-and-unpacking-data" title="Permalink to this headline"></a></h2>
<p>Each record in a .rec file can contain arbitrary binary data, but machine
learning data typically has a label/data structure. <code class="docutils literal"><span class="pre">mx.recordio</span></code> also contains
a few utility functions for packing such data, namely: <code class="docutils literal"><span class="pre">pack</span></code>, <code class="docutils literal"><span class="pre">unpack</span></code>,
<code class="docutils literal"><span class="pre">pack_img</span></code>, and <code class="docutils literal"><span class="pre">unpack_img</span></code>.</p>
<div class="section" id="binary-data">
<span id="binary-data"></span><h3>Binary Data<a class="headerlink" href="#binary-data" title="Permalink to this headline"></a></h3>
<p><code class="docutils literal"><span class="pre">pack</span></code> and <code class="docutils literal"><span class="pre">unpack</span></code> are used for storing float (or 1d array of float) label and
binary data:</p>
<ul class="simple">
<li>pack:</li>
</ul>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="c1"># pack</span>
<span class="n">data</span> <span class="o">=</span> <span class="s1">'data'</span>
<span class="n">label1</span> <span class="o">=</span> <span class="mf">1.0</span>
<span class="n">header1</span> <span class="o">=</span> <span class="n">mx</span><span class="o">.</span><span class="n">recordio</span><span class="o">.</span><span class="n">IRHeader</span><span class="p">(</span><span class="n">flag</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span> <span class="n">label</span><span class="o">=</span><span class="n">label1</span><span class="p">,</span> <span class="nb">id</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">id2</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span>
<span class="n">s1</span> <span class="o">=</span> <span class="n">mx</span><span class="o">.</span><span class="n">recordio</span><span class="o">.</span><span class="n">pack</span><span class="p">(</span><span class="n">header1</span><span class="p">,</span> <span class="n">data</span><span class="p">)</span>
<span class="k">print</span><span class="p">(</span><span class="s1">'float label:'</span><span class="p">,</span> <span class="nb">repr</span><span class="p">(</span><span class="n">s1</span><span class="p">))</span>
<span class="n">label2</span> <span class="o">=</span> <span class="p">[</span><span class="mf">1.0</span><span class="p">,</span> <span class="mf">2.0</span><span class="p">,</span> <span class="mf">3.0</span><span class="p">]</span>
<span class="n">header2</span> <span class="o">=</span> <span class="n">mx</span><span class="o">.</span><span class="n">recordio</span><span class="o">.</span><span class="n">IRHeader</span><span class="p">(</span><span class="n">flag</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span> <span class="n">label</span><span class="o">=</span><span class="n">label2</span><span class="p">,</span> <span class="nb">id</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">id2</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span>
<span class="n">s2</span> <span class="o">=</span> <span class="n">mx</span><span class="o">.</span><span class="n">recordio</span><span class="o">.</span><span class="n">pack</span><span class="p">(</span><span class="n">header2</span><span class="p">,</span> <span class="n">data</span><span class="p">)</span>
<span class="k">print</span><span class="p">(</span><span class="s1">'array label:'</span><span class="p">,</span> <span class="nb">repr</span><span class="p">(</span><span class="n">s2</span><span class="p">))</span>
</pre></div>
</div>
<ul class="simple">
<li>unpack:</li>
</ul>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="k">print</span><span class="p">(</span><span class="o">*</span><span class="n">mx</span><span class="o">.</span><span class="n">recordio</span><span class="o">.</span><span class="n">unpack</span><span class="p">(</span><span class="n">s1</span><span class="p">))</span>
<span class="k">print</span><span class="p">(</span><span class="o">*</span><span class="n">mx</span><span class="o">.</span><span class="n">recordio</span><span class="o">.</span><span class="n">unpack</span><span class="p">(</span><span class="n">s2</span><span class="p">))</span>
</pre></div>
</div>
</div>
<div class="section" id="image-data">
<span id="image-data"></span><h3>Image Data<a class="headerlink" href="#image-data" title="Permalink to this headline"></a></h3>
<p><code class="docutils literal"><span class="pre">pack_img</span></code> and <code class="docutils literal"><span class="pre">unpack_img</span></code> are used for packing image data. Records packed by
<code class="docutils literal"><span class="pre">pack_img</span></code> can be loaded by <code class="docutils literal"><span class="pre">mx.io.ImageRecordIter</span></code>.</p>
<ul class="simple">
<li>pack images</li>
</ul>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">data</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">ones</span><span class="p">((</span><span class="mi">3</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">),</span> <span class="n">dtype</span><span class="o">=</span><span class="n">np</span><span class="o">.</span><span class="n">uint8</span><span class="p">)</span>
<span class="n">label</span> <span class="o">=</span> <span class="mf">1.0</span>
<span class="n">header</span> <span class="o">=</span> <span class="n">mx</span><span class="o">.</span><span class="n">recordio</span><span class="o">.</span><span class="n">IRHeader</span><span class="p">(</span><span class="n">flag</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span> <span class="n">label</span><span class="o">=</span><span class="n">label</span><span class="p">,</span> <span class="nb">id</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span> <span class="n">id2</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span>
<span class="n">s</span> <span class="o">=</span> <span class="n">mx</span><span class="o">.</span><span class="n">recordio</span><span class="o">.</span><span class="n">pack_img</span><span class="p">(</span><span class="n">header</span><span class="p">,</span> <span class="n">data</span><span class="p">,</span> <span class="n">quality</span><span class="o">=</span><span class="mi">100</span><span class="p">,</span> <span class="n">img_fmt</span><span class="o">=</span><span class="s1">'.jpg'</span><span class="p">)</span>
<span class="k">print</span><span class="p">(</span><span class="nb">repr</span><span class="p">(</span><span class="n">s</span><span class="p">))</span>
</pre></div>
</div>
<ul class="simple">
<li>unpack images</li>
</ul>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="k">print</span><span class="p">(</span><span class="o">*</span><span class="n">mx</span><span class="o">.</span><span class="n">recordio</span><span class="o">.</span><span class="n">unpack_img</span><span class="p">(</span><span class="n">s</span><span class="p">))</span>
</pre></div>
</div>
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<h3><a href="../../index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Record IO - Pack free-format data in binary files</a><ul>
<li><a class="reference internal" href="#mxrecordio">MXRecordIO</a></li>
<li><a class="reference internal" href="#mxindexedrecordio">MXIndexedRecordIO</a></li>
<li><a class="reference internal" href="#packing-and-unpacking-data">Packing and Unpacking Data</a><ul>
<li><a class="reference internal" href="#binary-data">Binary Data</a></li>
<li><a class="reference internal" href="#image-data">Image Data</a></li>
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