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PORuby weirdness: x == y && [x, y].uniq == [x, y]
 

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    <p>I have an two-element array of ActiveRecord objects, <code>slots_to_import</code>. These objects have <code>begin_at</code> columns, and thus attributes. I was trying to get objects that have unique <code>begin_at</code> values. Alas, <code>slots_to_import.uniq_by(&amp;:begin_at)</code> did not work. But the <code>begin_at</code> values are equal for the two objects:</p> <pre><code>(rdb:1) p slots_to_import.first.begin_at == slots_to_import.last.begin_at true (rdb:1) p slots_to_import.uniq_by(&amp;:begin_at).map(&amp;:begin_at) [Mon, 26 Nov 2012 19:00:00 UTC +00:00, Mon, 26 Nov 2012 19:00:00 UTC +00:00] (rdb:1) p [slots_to_import.first.begin_at, slots_to_import.last.begin_at].uniq [Mon, 26 Nov 2012 19:00:00 UTC +00:00, Mon, 26 Nov 2012 19:00:00 UTC +00:00] </code></pre> <p>Some more checking around:</p> <pre><code>(rdb:1) p [slots_to_import.first.begin_at.to_datetime, slots_to_import.last.begin_at.to_datetime].uniq [Mon, 26 Nov 2012 19:00:00 +0000] (rdb:1) p [slots_to_import.first.begin_at.usec, slots_to_import.last.begin_at.usec].uniq [0] (rdb:1) p [slots_to_import.first.begin_at.to_f, slots_to_import.last.begin_at.to_f].uniq [1353956400.0] (rdb:1) p [slots_to_import.first.begin_at.utc, slots_to_import.last.begin_at.utc].uniq [Mon, 26 Nov 2012 19:00:00 +0000] (rdb:1) p [slots_to_import.first.begin_at, slots_to_import.last.begin_at].uniq [Mon, 26 Nov 2012 19:00:00 UTC +00:00, Mon, 26 Nov 2012 19:00:00 UTC +00:00] </code></pre> <p>I thought perhaps that uniq was checking whether they were the same object (since they were not). But no, some noodling in my rails console showed me that it does not use an object id check:</p> <pre><code>1.8.7 :111 &gt; x = Time.zone.parse("Mon, 29 Oct 2012 19:29:17 UTC +00:00") =&gt; Mon, 29 Oct 2012 19:29:17 UTC +00:00 1.8.7 :112 &gt; y = Time.zone.parse("Mon, 29 Oct 2012 19:29:17 UTC +00:00") =&gt; Mon, 29 Oct 2012 19:29:17 UTC +00:00 1.8.7 :113 &gt; x == y =&gt; true 1.8.7 :114 &gt; [x, y].uniq =&gt; [Mon, 29 Oct 2012 19:29:17 UTC +00:00] </code></pre> <p>I'm using Ruby 1.8.7p358 and ActiveSupport 3.2.0. BTW, I can solve my own issue by simply adding a <code>to_datetime</code>, but I'm really curious why this isn't working without a conversion.</p>
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    1. COHave you tried comparing the results of `x.hash` and `y.hash`?
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    2. CO@hammar: That's an interesting idea seeing as `uniq_by` is Hash based.
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    3. CO@hammar `x.hash` and `y.hash` are also equal! - `(rdb:1) p slots_to_import.first.begin_at.hash == slots_to_import.last.begin_at.hash => true`
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