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I have an array as below

[{
        "id": "001",
        "name": "A",
        "timestamp_created": "2019-02-27T11:22:19"
    },
    {
        "id": "002",
        "name": "A",
        "timestamp_created": "2019-02-27T11:30:19"
    },
    {
        "id": "003",
        "name": "B",
        "timestamp_created": "2019-02-27T10:15:19"
    },
    {
        "id": "004",
        "name": "B",
        "timestamp_created": "2019-02-27T11:05:19"
    }
]

I want to create a new array based on the above array, but with only latest item, (group by name of item).

 [{
            "id": "002",
            "name": "A",
            "timestamp_created": "2019-02-27T11:30:19"
        },
        {
            "id": "004",
            "name": "B",
            "timestamp_created": "2019-02-27T11:05:19"
        }
    ]

How to bine different Lodash's features to achieve the result?

Any suggestion, please help me.

I have an array as below

[{
        "id": "001",
        "name": "A",
        "timestamp_created": "2019-02-27T11:22:19"
    },
    {
        "id": "002",
        "name": "A",
        "timestamp_created": "2019-02-27T11:30:19"
    },
    {
        "id": "003",
        "name": "B",
        "timestamp_created": "2019-02-27T10:15:19"
    },
    {
        "id": "004",
        "name": "B",
        "timestamp_created": "2019-02-27T11:05:19"
    }
]

I want to create a new array based on the above array, but with only latest item, (group by name of item).

 [{
            "id": "002",
            "name": "A",
            "timestamp_created": "2019-02-27T11:30:19"
        },
        {
            "id": "004",
            "name": "B",
            "timestamp_created": "2019-02-27T11:05:19"
        }
    ]

How to bine different Lodash's features to achieve the result?

Any suggestion, please help me.

• javascript
• arrays
• lodash

Share Improve this question Follow edited Feb 28, 2019 at 9:15 Chamila Maddumage 3,88622 gold badges3434 silver badges4444 bronze badges asked Feb 27, 2019 at 15:19 Phong VuPhong Vu 2,89666 gold badges2727 silver badges5353 bronze badges 2

• Latest two items? Latest item of each name What? – mplungjan Commented Feb 27, 2019 at 15:21
• As example, array has 2 items (A,B) but different timestamp created, I wanna create a new array with latest A and latest B, depend on timestamp – Phong Vu Commented Feb 27, 2019 at 15:24

Add a ment  | 

5 Answers 5

Sorted by: Reset to default 2

You could take Map, collect all latest items (by checking timestamp_created), grouped by name and get the values.

var data = [{ id: "002", name: "A", timestamp_created: "2019-02-27T11:30:19" }, { id: "003", name: "B", timestamp_created: "2019-02-27T10:15:19" }, { id: "004", name: "B", timestamp_created: "2019-02-27T11:05:19" }, { id: "001", name: "A", timestamp_created: "2019-02-27T11:22:19" }],
    result = Array.from(data
        .reduce(
            (m, o) => m.has(o.name) && m.get(o.name).timestamp_created > o.timestamp_created
               ? m
               : m.set(o.name, o),
            new Map
        )
        .values()
    );
    
console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Without using the library lodash, you can generate the result using Array.reduce():

const input = [
    {
        "id": "001",
        "name": "A",
        "timestamp_created": "2019-02-27T11:22:19"
    },
    {
        "id": "002",
        "name": "A",
        "timestamp_created": "2019-02-27T11:30:19"
    },
    {
        "id": "003",
        "name": "B",
        "timestamp_created": "2019-02-27T10:15:19"
    },
    {
        "id": "004",
        "name": "B",
        "timestamp_created": "2019-02-27T11:05:19"
    }
];

let res = input.reduce((acc, {id, name, timestamp_created}) =>
{
    acc[name] = acc[name] || {id, name, timestamp_created};
    
    if (acc[name].timestamp_created < timestamp_created)
        acc[name] = {id, name, timestamp_created};    

    return acc;
}, {});

console.log(Object.values(res));

.as-console {background-color:black !important; color:lime;}
.as-console-wrapper {max-height:100% !important; top:0;}

Great answers so far. As OP asked for a Lodash solution, here's that:

const data = [{
    "id": "001",
    "name": "A",
    "timestamp_created": "2019-02-27T11:22:19"
},
{
    "id": "002",
    "name": "A",
    "timestamp_created": "2019-02-27T11:30:19"
},
{
    "id": "003",
    "name": "B",
    "timestamp_created": "2019-02-27T10:15:19"
},
{
    "id": "004",
    "name": "B",
    "timestamp_created": "2019-02-27T11:05:19"
}
];

const reduceFunction = (acc, val) => {
    if (val.name in acc) {
        if (val.timestamp_created > acc[val.name].timestamp_created) {
            acc[val.name] = val
        }
    } else {
        acc[val.name] = val
    }

    return acc;
};

const filteredData = _.values(
    _.reduce(data, reduceFunction, {})
);

If you want to use lodash this will do the job.

function latestItems(original) {
    filtered = [];
    grouped = _.groupBy(original, "name");
    _.forEach(grouped, function (group) {
        newest = {
            "timestamp_created": "0"
        };
        _.forEach(group, function (item) {
            if (item.timestamp_created > newest.timestamp_created) {
                newest = item;
            }
        });
        filtered.push(newest);
    });

    return filtered;
}

Short solution using lodash

const data = [...]
const result = _(data)
  .groupBy('name')
  .map(group => _.maxBy(group, 'timestamp_created'))
  .value()

---

Use groupBy to group by name. Then use maxBy to get object that has max timestamp_created.

_.maxBy(array, [iteratee=_.identity])

This method is like _.max except that it accepts iteratee which is invoked for each element in array to generate the criterion by which the value is ranked. The iteratee is invoked with one argument: (value).

https://lodash./docs/4.17.11#maxBy

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