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df-research/tech.ml.dataset/docs/javadoc/tech/v3/dataset/Arrow.html
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<pre>public class <span class="typeNameLabel">Arrow</span>
extends java.lang.Object</pre>
<div class="block"><p>Bindings to save/load datasets apache arrow streaming format. These bindings support JDK-17, memory mapping, and per-column compression.</p>
<p>Required Dependencies:</p>
<pre><code class="clojure">[org.apache.arrow/arrow-vector &quot;6.0.0&quot;]
[org.lz4/lz4-java &quot;1.8.0&quot;]
[com.github.luben/zstd-jni &quot;1.5.1-1&quot;]
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<td class="colFirst"><code>static void</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../tech/v3/dataset/Arrow.html#datasetSeqToStream-java.lang.Iterable-java.lang.Object-java.lang.Object-">datasetSeqToStream</a></span>(java.lang.Iterable&nbsp;dsSeq,
java.lang.Object&nbsp;pathOrInputStream,
java.lang.Object&nbsp;options)</code>
<div class="block">Save a sequence of datasets to a single stream file.</div>
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<td class="colFirst"><code>static void</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../tech/v3/dataset/Arrow.html#datasetToStream-java.lang.Object-java.lang.Object-java.lang.Object-">datasetToStream</a></span>(java.lang.Object&nbsp;ds,
java.lang.Object&nbsp;pathOrInputStream,
java.lang.Object&nbsp;options)</code>
<div class="block">Save a dataset to apache stream format.</div>
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<td class="colFirst"><code>static java.util.Map</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../tech/v3/dataset/Arrow.html#streamtoDataset-java.lang.Object-java.lang.Object-">streamtoDataset</a></span>(java.lang.Object&nbsp;pathOrInputStream,
java.lang.Object&nbsp;options)</code>
<div class="block">Load an apache arrow streaming file returning a single dataset.</div>
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<td class="colFirst"><code>static java.lang.Iterable</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../tech/v3/dataset/Arrow.html#streamToDatasetSeq-java.lang.Object-java.lang.Object-">streamToDatasetSeq</a></span>(java.lang.Object&nbsp;pathOrInputStream,
java.lang.Object&nbsp;options)</code>
<div class="block">Load an apache arrow streaming file returning a sequence of datasets, one for each record batch.</div>
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<pre>public static&nbsp;void&nbsp;datasetToStream(java.lang.Object&nbsp;ds,
java.lang.Object&nbsp;pathOrInputStream,
java.lang.Object&nbsp;options)</pre>
<div class="block"><p>Save a dataset to apache stream format.</p>
<p>Options:</p>
<ul>
<li>
<p><code>strings-as-text?</code>: - defaults to false - Save out strings into arrow files without dictionaries. This works well if you want to load an arrow file in-place or if you know the strings in your dataset are either really large or should not be in string tables.</p></li>
<li>
<p><code>:compression</code> - Either <code>:zstd</code> or <code>:lz4</code>, defaults to no compression (nil). Per-column compression of the data can result in some significant size savings (2x+) and thus some significant time savings when transferring over the network. Using compression makes loading via mmap non-in-place - If you are going to use compression mmap probably doesn&rsquo;t make sense on load and most likely will result on slower loading times. Zstd can also be passed in map form with an addition parameter, <code>:level</code> which defaults to 3.</p></li>
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<pre><code class="java">//Slightly higher compression than the default.
datasetToStream(ds, &quot;data.arrow-ipc&quot;, hashmap(kw(&quot;compression&quot;),
hashmap(kw(&quot;compression-type&quot;), kw(&quot;zstd&quot;),
kw(&quot;level&quot;), 5)));
</code></pre></div>
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<h4>datasetSeqToStream</h4>
<pre>public static&nbsp;void&nbsp;datasetSeqToStream(java.lang.Iterable&nbsp;dsSeq,
java.lang.Object&nbsp;pathOrInputStream,
java.lang.Object&nbsp;options)</pre>
<div class="block"><p>Save a sequence of datasets to a single stream file. Datasets must either have matching schemas or downstream dataset column datatypes must be able to be widened to the initial dataset column datatypes.</p>
<p>For options see <code>datasetToStream</code>.</p></div>
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<h4>streamtoDataset</h4>
<pre>public static&nbsp;java.util.Map&nbsp;streamtoDataset(java.lang.Object&nbsp;pathOrInputStream,
java.lang.Object&nbsp;options)</pre>
<div class="block"><p>Load an apache arrow streaming file returning a single dataset. File must only contain a single record batch.</p>
<p>Options:</p>
<ul>
<li>
<p><code>:open-type</code> - Either <code>:mmap</code> or <code>:input-stream</code> defaulting to the slower but more robust <code>:input-stream</code> pathway. When using <code>:mmap</code> resources will be released when the resource system dictates - see documentation for <a href="https://cnuernber.github.io/dtype-next/javadoc/index.html">tech.v3.DType.stackResourceContext</a>. When using <code>:input-stream</code> the stream will be closed when the lazy sequence is either fully realized or an exception is thrown.</p></li>
<li>
<p><code>close-input-stream?</code> - When using <code>:input-stream</code> <code>:open-type</code>, close the input stream upon exception or when stream is fully realized. Defaults to true.</p></li>
<li>
<p><code>:integer-datatime-types?</code> - when true arrow columns in the appropriate packed datatypes will be represented as their integer types as opposed to their respective packed types. For example columns of type <code>:epoch-days</code> will be returned to the user as datatype <code>:epoch-days</code> as opposed to <code>:packed-local-date</code>. This means reading values will return integers as opposed to <code>java.time.LocalDate</code>s.</p></li>
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<pre>public static&nbsp;java.lang.Iterable&nbsp;streamToDatasetSeq(java.lang.Object&nbsp;pathOrInputStream,
java.lang.Object&nbsp;options)</pre>
<div class="block"><p>Load an apache arrow streaming file returning a sequence of datasets, one for each record batch. For options see streamToDataset.</p></div>
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