Is it possible to group by multiple dimensions in crossfilter?

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囚心锁ツ
囚心锁ツ 2021-02-02 03:36

For Example If we have data for books, authors and date information. Can we build a crossfilter for how many books are present for author per month?

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  •  悲&欢浪女
    2021-02-02 03:51

    In pseudo sql terms, what you are trying to do is:

    SELECT COUNT(book)
    GROUP BY author, month
    

    The way I approach this type of problem is to 'group' the fields together into a single dimension. So in your case I would concatenate the month and author information together, into a dimension.

    Let this be our test data:

    var cf = crossfilter([
    { date:"1 jan 2014", author: "Mr X", book: "Book 1" },
    { date:"2 jan 2014", author: "Mr X", book: "Book 2" },
    { date:"3 feb 2014", author: "Mr X", book: "Book 3" },
    { date:"1 mar 2014", author: "Mr X", book: "Book 4" },
    { date:"2 apr 2014", author: "Mr X", book: "Book 5" },
    { date:"3 apr 2014", author: "Mr X", book: "Book 6"},
    { date:"1 jan 2014", author: "Ms Y", book: "Book 7" },
    { date:"2 jan 2014", author: "Ms Y", book: "Book 8" },
    { date:"3 jan 2014", author: "Ms Y", book: "Book 9" },
    { date:"1 mar 2014", author: "Ms Y", book: "Book 10" },
    { date:"2 mar 2014", author: "Ms Y", book: "Book 11" },
    { date:"3 mar 2014", author: "Ms Y", book: "Book 12" },
    { date:"4 apr 2014", author: "Ms Y", book: "Book 13" }
    ]);  
    

    The dimension is defined as follows:

    var dimensionMonthAuthor = cf.dimension(function (d) {
      var thisDate = new Date(d.date);
      return 'month='+thisDate.getMonth()+';author='+d.author;
    });
    

    And now we can just simply do a reduce count to calculate how many books there are per author, per month (i.e. per dimension unit):

    var monthAuthorCount = dimensionMonthAuthor.group().reduceCount(function (d) { return d.book; }).all();
    

    And the results are as follows:

    {"key":"month=0;author=Mr X","value":2}
    {"key":"month=0;author=Ms Y","value":3}
    {"key":"month=1;author=Mr X","value":1}
    {"key":"month=2;author=Mr X","value":1}
    {"key":"month=2;author=Ms Y","value":3}
    {"key":"month=3;author=Mr X","value":2}
    {"key":"month=3;author=Ms Y","value":1}
    

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