| <!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Infer the fields of a JSON file by reading the first n records of the buffer, with `max_read_records` controlling the maximum number of records to read."><title>infer_json_schema in arrow_json::reader::schema - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-46f98efaafac5295.ttf.woff2,FiraSans-Regular-018c141bf0843ffd.woff2,FiraSans-Medium-8f9a781e4970d388.woff2,SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2,SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2" crossorigin href="../../../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../../../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../../../static.files/rustdoc-dd39b87e5fcfba68.css"><meta name="rustdoc-vars" data-root-path="../../../" data-static-root-path="../../../static.files/" data-current-crate="arrow_json" data-themes="" data-resource-suffix="" data-rustdoc-version="1.80.0-nightly (8c127df75 2024-05-16)" data-channel="nightly" data-search-js="search-d52510db62a78183.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../../../static.files/storage-118b08c4c78b968e.js"></script><script defer src="sidebar-items.js"></script><script defer src="../../../static.files/main-20a3ad099b048cf2.js"></script><noscript><link rel="stylesheet" href="../../../static.files/noscript-df360f571f6edeae.css"></noscript><link rel="alternate icon" type="image/png" href="../../../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../../../static.files/favicon-2c020d218678b618.svg"></head><body class="rustdoc fn"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle" title="show sidebar"></button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../../arrow_json/index.html">arrow_json</a><span class="version">51.0.0</span></h2></div><div class="sidebar-elems"><h2><a href="index.html">In arrow_json::reader::schema</a></h2></div></nav><div class="sidebar-resizer"></div><main><div class="width-limiter"><rustdoc-search></rustdoc-search><section id="main-content" class="content"><div class="main-heading"><h1>Function <a href="../../index.html">arrow_json</a>::<wbr><a href="../index.html">reader</a>::<wbr><a href="index.html">schema</a>::<wbr><a class="fn" href="#">infer_json_schema</a><button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><span class="out-of-band"><a class="src" href="../../../src/arrow_json/reader/schema.rs.html#270-277">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>−</span>]</button></span></div><pre class="rust item-decl"><code>pub fn infer_json_schema<R: <a class="trait" href="https://doc.rust-lang.org/nightly/std/io/trait.BufRead.html" title="trait std::io::BufRead">BufRead</a>>( |
| reader: R, |
| max_read_records: <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a><<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a>> |
| ) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><(Schema, <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a>), ArrowError></code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Infer the fields of a JSON file by reading the first n records of the buffer, with |
| <code>max_read_records</code> controlling the maximum number of records to read.</p> |
| <p>If <code>max_read_records</code> is not set, the whole file is read to infer its field types.</p> |
| <p>Returns inferred schema and number of records read.</p> |
| <p>This function will not seek back to the start of the <code>reader</code>. The user has to manage the |
| original file’s cursor. This function is useful when the <code>reader</code>’s cursor is not available |
| (does not implement <a href="https://doc.rust-lang.org/nightly/std/io/trait.Seek.html" title="trait std::io::Seek"><code>Seek</code></a>), such is the case for compressed streams decoders.</p> |
| <h2 id="examples"><a class="doc-anchor" href="#examples">§</a>Examples</h2> |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>std::fs::File; |
| <span class="kw">use </span>std::io::{BufReader, SeekFrom, Seek}; |
| <span class="kw">use </span>flate2::read::GzDecoder; |
| <span class="kw">use </span>arrow_json::reader::infer_json_schema; |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>file = File::open(<span class="string">"test/data/mixed_arrays.json.gz"</span>).unwrap(); |
| |
| <span class="comment">// file's cursor's offset at 0 |
| </span><span class="kw">let </span><span class="kw-2">mut </span>reader = BufReader::new(GzDecoder::new(<span class="kw-2">&</span>file)); |
| <span class="kw">let </span>inferred_schema = infer_json_schema(<span class="kw-2">&mut </span>reader, <span class="prelude-val">None</span>).unwrap(); |
| <span class="comment">// cursor's offset at end of file |
| |
| // seek back to start so that the original file is usable again |
| </span>file.seek(SeekFrom::Start(<span class="number">0</span>)).unwrap();</code></pre></div> |
| </div></details></section></div></main></body></html> |
