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JamieMason/group-objects-by-property.md

Created September 14, 2018 07:38
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  1. JamieMason created this gist Sep 14, 2018.
    112 changes: 112 additions & 0 deletions group-objects-by-property.md
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    # Group Array of JavaScript Objects by Key or Property Value

    ## Implementation

    ```js
    const groupBy = key => array =>
    array.reduce((objectsByKeyValue, obj) => {
    const value = obj[key];
    objectsByKeyValue[value] = (objectsByKeyValue[value] || []).concat(obj);
    return objectsByKeyValue;
    }, {});
    ```

    Or using an implicit return (slower):

    ```js
    const groupBy = key => array =>
    array.reduce(
    (objectsByKeyValue, obj) => ({
    ...objectsByKeyValue,
    [obj[key]]: (objectsByKeyValue[obj[key]] || []).concat(obj)
    }),
    {}
    );
    ```

    ## Usage

    ```js
    const cars = [
    { brand: 'Audi', color: 'black' },
    { brand: 'Audi', color: 'white' },
    { brand: 'Ferarri', color: 'red' },
    { brand: 'Ford', color: 'white' },
    { brand: 'Peugot', color: 'white' }
    ];

    const groupByBrand = groupBy('brand');
    const groupByColor = groupBy('color');

    console.log(
    JSON.stringify({
    carsByBrand: groupByBrand(cars),
    carsByColor: groupByColor(cars)
    }, null, 2)
    );
    ```

    ### Output

    ```json
    {
    "carsByBrand": {
    "Audi": [
    {
    "brand": "Audi",
    "color": "black"
    },
    {
    "brand": "Audi",
    "color": "white"
    }
    ],
    "Ferarri": [
    {
    "brand": "Ferarri",
    "color": "red"
    }
    ],
    "Ford": [
    {
    "brand": "Ford",
    "color": "white"
    }
    ],
    "Peugot": [
    {
    "brand": "Peugot",
    "color": "white"
    }
    ]
    },
    "carsByColor": {
    "black": [
    {
    "brand": "Audi",
    "color": "black"
    }
    ],
    "white": [
    {
    "brand": "Audi",
    "color": "white"
    },
    {
    "brand": "Ford",
    "color": "white"
    },
    {
    "brand": "Peugot",
    "color": "white"
    }
    ],
    "red": [
    {
    "brand": "Ferarri",
    "color": "red"
    }
    ]
    }
    }
    ```