Sorting an array of objects with multiple entries

Question

I would like to rearrange an array of objects in javascript, which looks like this:

[{ year: "1950-12-20", product: ["product 1", "product 2, "product 3"] }, { year: "1951-12-20", product: ["product 3", "product 2"] }, { year: "1952-12-20", product: ["product 3", "product 4"] }]

so that I get two arrays, one with the products and one with the years when they appear.

a = ["product 1", "product 2", "product 3", "product 4"]
b = ["1950-12-20", [ "1950-12-20, "1951-12-20"],["1950-12-20", "1951-12-20", "1952-12-20"],"1952-12-20"]

I have tried to loop through each object through nestled for-loops, but how do I treat the array of strings in the object array in a nice way?

What does "treat the array of strings in the object array in a nice way?" mean? What is wrong with what you have now? — Marcin
– Marcin, Commented Nov 29, 2012 at 14:56
@Marcin: I have tried to map the data so that I have an array like this: data = [["1950-12-20", ["product 1", "product 2, "product 3"]],...], and then a for-loop: for ( var i = 0; i < data.length; i++ ) { for ( var j = 0; j < data[i][1].length; j++ ) {} }. Inside the for-loops I try to add the new products to an array using .push. — graphmeter
– graphmeter, Commented Nov 29, 2012 at 15:05

Samuel Caillerie · Accepted Answer · 2012-11-29 15:10:55Z

1

I don't know what kind of loop you have tested, but this type of code is not so long for what has to be done :

var data = [{ year: "1950-12-20", product: ["product 1", "product 2", "product 3"] }, { year: "1951-12-20", product: ["product 3", "product 2"] }, { year: "1952-12-20", product: ["product 3", "product 4"] }];

var nbData = data.length, iData;
var years = [], products = [], dictProductsYear = {};
var nbProducts, iProduct, p;


// Loop through years
for(iData = 0; iData < nbData; iData ++) {
    products = data[iData].product;
    nbProducts = products.length;

    // Add the current year to the concerned products
    for(iProduct = 0; iProduct < nbProducts; iProduct ++) {
        p = products[iProduct];

        // Registered product
        if(dictProductsYear[p]) dictProductsYear[p].push(data[iData].year);
        // Unregistered one
        else dictProductsYear[p] = [ data[iData].year ];
    }
}

var yearList = [], productList = [];

// Flatten the dictionary in 2 lists
for(p in dictProductsYear) {
    productList.push(p);
    yearList.push(dictProductsYear[p]);
}

answered Nov 29, 2012 at 15:10

Samuel Caillerie

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1 Comment

graphmeter Over a year ago

Thanks. I tried to generate an array using .map of the object array, but this much nicer to keep the array of objects intact. I will try it out.

Bergi · Accepted Answer · 2012-11-29 15:30:55Z

1

This looks a bit like @Samuel Caillerie's code, but is more concise:

var data = [{ year: "1950-12-20", product: ["product 1", "product 2", "product 3"] }, { year: "1951-12-20", product: ["product 3", "product 2"] }, { year: "1952-12-20", product: ["product 3", "product 4"] }];

var yearsByProd = {};
for (var i=0; i<data.length; i++) {
    var prod = data[i].product;
    for (var j=0; j<prod.length; j++) {
         if (prod[j] in yearsByProd)
             yearsByProd[prod[j]].push(data[i].year);
         else
             yearsByProd[prod[j]] = [data[i].year];
    }
}
var a, b;
b = (a = Object.keys(yearsByProd).sort()).map(function(prod) {
    // add an if-else-statement here if you want to extract single years from their array
    return yearsByProd[prod];
});

edited Nov 29, 2012 at 15:30

answered Nov 29, 2012 at 15:24

Bergi

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3 Comments

Samuel Caillerie Over a year ago

Yes, but be careful that Object.keys and Array.prototype.map are not implemented cross-browser (see MDN Object.keys and MDN Array.prototype.map respectively, not for IE<9 for example).

graphmeter Over a year ago

@Bergi: Works very well, but I think I will need support for IE < 9.

Bergi Over a year ago

@SamuelCaillerie: Yeah, should've mentioned that. Thanks for the links to the shims, most complainers don't mention them :-)

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