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Using date as a hash table key

How to create a hash table object in JavaSript and use a date as a key? So far I have this:

var eventHash = {};
for (var i = 0, l = events.length; i < l; i += 1) {
    eventHash[events[i].date.getTime()] = events[i];
}

And then, when I want to find an event related to today, I would use this:

var event = eventHash[(new Date(2011, 04, 26, 0, 0, 0, 0)).getTime()];

Can anyone see any pitfalls with this solution or any suggestions for improvement?

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3 answers

Why don't you just use the date representation in ISO8601 format, so the key will look like 20110426. Creating a date object seems a bit inefficient.

It would also make debugging easier, as property names are more readable for people, even if you also add hhmmss.

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, , , , . .

: 23 , 26 :)

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I have a somewhat similar problem, and my solution may help others.

I have a list of "records", each record has a timestamp and value. I want to divide them into buckets, one for each day. In Python, I would use collection.defaultdict, but since JavaScript does not have something like this, I do the following.

If you want to read keys, remember that when using a date as a key object, it is converted as a string.

var get_entries = function() {
    var entries = [];
    entries.push({
        'timestamp': 1381831606,
        'value': 3
    });
    entries.push({
        'timestamp': 1381831406,
        'value': 2
    });
    entries.push({
        'timestamp': 1381531606,
        'value': 6
    });
    entries.push({
        'timestamp': 1381221606,
        'value': 9
    });
    entries.push({
        'timestamp': 1381221601,
        'value': 8
    });
    entries.push({
        'timestamp': 1381221656,
        'value': 7
    });
    return entries;
};

var normalize_date = function(timestamp) {
    // JavaScript timestamps work with milliseconds.
    var dt = new Date(timestamp * 1000);
    return new Date(
        dt.getFullYear(),
        dt.getMonth(),
        dt.getDate()
    );
};

var prepare_data = function() {
    var entry,
        line = {};
    var entries_raw = get_entries();
    for (var i = 0; i < entries_raw.length; i++) {
        entry = entries_raw[i];
        entry.date = normalize_date(entries_raw[i].timestamp);
        // If date not exists in line, create it.
        console.log('Found entry for date', entry.date, 'with value', entry.value);
        if (typeof(line[entry.date]) === 'undefined'){
           line[entry.date] = 0;
        }
        line[entry.date] += entry.value;
    }
    console.log(line);
    return line;
};

prepare_data();

Conclusion:

$ nodejs diaryindex.js
Found entry for date Tue Oct 15 2013 00:00:00 GMT+0200 (CEST) with value 3
Found entry for date Tue Oct 15 2013 00:00:00 GMT+0200 (CEST) with value 2
Found entry for date Sat Oct 12 2013 00:00:00 GMT+0200 (CEST) with value 6
Found entry for date Tue Oct 08 2013 00:00:00 GMT+0200 (CEST) with value 9
Found entry for date Tue Oct 08 2013 00:00:00 GMT+0200 (CEST) with value 8
Found entry for date Tue Oct 08 2013 00:00:00 GMT+0200 (CEST) with value 7
{ 'Tue Oct 15 2013 00:00:00 GMT+0200 (CEST)': 5,
  'Sat Oct 12 2013 00:00:00 GMT+0200 (CEST)': 6,
  'Tue Oct 08 2013 00:00:00 GMT+0200 (CEST)': 24 }
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