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POCouchDB function to sample records at a given interval.
 

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    <p>I have records with a time value and need to be able to query them for a span of time and return only records at a given interval. </p> <p>For example I may need all the records from 12:00 to 1:00 in 10 minute intervals giving me 12:00, 12:10, 12:20, 12:30, ... 12:50, 01:00. The interval needs to be a parameter and it may be any time value. 15 minutes, 47 seconds, 1.4 hours. </p> <p>I attempted to do this doing some kind of reduce but that is apparently the wrong place to do it. </p> <p>Here is what I have come up with. Comments are welcome. </p> <p>Created a view for the time field so I can query a range of times. The view outputs the id and the time.</p> <pre><code>function(doc) { emit([doc.rec_id, doc.time], [doc._id, doc.time]) } </code></pre> <p>Then I created a list function that accepts a param called interval. In the list function I work thru the rows and compare the current rows time to the last accepted time. If the span is greater or equal to the interval I add the row to the output and JSON-ify it. </p> <pre><code>function(head, req) { // default to 30000ms or 30 seconds. var interval = 30000; // get the interval from the request. if (req.query.interval) { interval = req.query.interval; } // setup var row; var rows = []; var lastTime = 0; // go thru the results... while (row = getRow()) { // if the time from view is more than the interval // from our last time then add it. if (row.value[1] - lastTime &gt; interval) { lastTime = row.value[1]; rows.push(row); } } // JSON-ify! send(JSON.stringify({'rows' : rows})); } </code></pre> <p>So far this is working well. I will test against some large data to see how the performance is. Any comments on how this could be done better or would this be the correct way with couch?</p>
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    1. USFredArters
    1. USFredArters
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    1. COYou may want to `parseInt(req.query.interval)`. I don't remember offhand but I *think* everything in req.query is a string.
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      1. USJasonSmith
 

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