return last occurrence of name (many names) in an array of objects

user_8216294 0
Viewed 73

Given the following data source:

[
  {
  "Username" : "Patrick",
  "Time" : "08:01:32",
  "Status" :  "log in"
  },
  {
  "Username" : "Patrick",
  "Time" : "08:34:31",
  "Status" :  "idle"
  },
  {
  "Username" : "Patrick",
  "Time" : "08:52:10",
  "Status" :  "meeting"
  },
  {
  "Username" : "Patrick",
  "Time" : "10:07:52",
  "Status" :  "daily tasks"
  },
  {
  "Username" : "Patrick",
  "Time" : "12:00:11",
  "Status" :  "lunch"
  },
  {
  "Username" : "Mark",
  "Time" : "07:40:32",
  "Status" :  "log in"
  },
  {
  "Username" : "Mark",
  "Time" : "08:54:31",
  "Status" :  "meeting"
  },
  {
  "Username" : "Mark",
  "Time" : "09:52:10",
  "Status" :  "idle"
  },
  {
  "Username" : "Mark",
  "Time" : "10:07:52",
  "Status" :  "daily tasks"
  },
  {
  "Username" : "Mark",
  "Time" : "12:30:11",
  "Status" :  "lunch"
  }
]

How do I get the last occurrence of each name in this array in a simple way? I was thinking about the filter function however I'm not sure how to proceed on this. Any support or tip will be highly appreciated.

The expected outcome should be as follows:

[
  {
  "Username" : "Patrick",
  "Time" : "12:00:11",
  "Status" :  "lunch"
  },
  {
  "Username" : "Mark",
  "Time" : "12:30:11",
  "Status" :  "lunch"
  }
]
arrays json javascript
4 Answers

Using ES6, you can reduce the array into a map, and then spread the values back to an array:

const data = [{"Username":"Patrick","Time":"08:01:32","Status":"log in"},{"Username":"Patrick","Time":"08:34:31","Status":"idle"},{"Username":"Patrick","Time":"08:52:10","Status":"meeting"},{"Username":"Patrick","Time":"10:07:52","Status":"daily tasks"},{"Username":"Patrick","Time":"12:00:11","Status":"lunch"},{"Username":"Mark","Time":"07:40:32","Status":"log in"},{"Username":"Mark","Time":"08:54:31","Status":"meeting"},{"Username":"Mark","Time":"09:52:10","Status":"idle"},{"Username":"Mark","Time":"10:07:52","Status":"daily tasks"},{"Username":"Mark","Time":"12:30:11","Status":"lunch"}];


const result = [...data.reduce((m, o) => m.set(o.Username, o), new Map()).values()];

console.log(result);

In ES5 you can reduce the array to an object that will contain the unique items, and then map the object back to an array using Object#keys:

var data = [{"Username":"Patrick","Time":"08:01:32","Status":"log in"},{"Username":"Patrick","Time":"08:34:31","Status":"idle"},{"Username":"Patrick","Time":"08:52:10","Status":"meeting"},{"Username":"Patrick","Time":"10:07:52","Status":"daily tasks"},{"Username":"Patrick","Time":"12:00:11","Status":"lunch"},{"Username":"Mark","Time":"07:40:32","Status":"log in"},{"Username":"Mark","Time":"08:54:31","Status":"meeting"},{"Username":"Mark","Time":"09:52:10","Status":"idle"},{"Username":"Mark","Time":"10:07:52","Status":"daily tasks"},{"Username":"Mark","Time":"12:30:11","Status":"lunch"}];

var uniques = data.reduce(function(m, o) {
  m[o.Username] = o;
  
  return m;
}, Object.create(null));

var result = Object.keys(uniques).map(function(key) {
  return uniques[key];
});

console.log(result);

user_51574540

You could use a hash table and use an explicit check if the time is greater than the last time of the inserted object.

This proposal works with unsorted data as well.

var data = [{ Username: "Patrick", Time: "08:01:32", Status: "log in" }, { Username: "Patrick", Time: "08:34:31", Status: "idle" }, { Username: "Patrick", Time: "08:52:10", Status: "meeting" }, { Username: "Patrick", Time: "10:07:52", Status: "daily tasks" }, { Username: "Patrick", Time: "12:00:11", Status: "lunch" }, { Username: "Mark", Time: "07:40:32", Status: "log in" }, { Username: "Mark", Time: "08:54:31", Status: "meeting" }, { Username: "Mark", Time: "09:52:10", Status: "idle" }, { Username: "Mark", Time: "10:07:52", Status: "daily tasks" }, { Username: "Mark", Time: "12:30:11", Status: "lunch" }],
    hash = Object.create(null),
    result = data.reduce(function (r, o) {
        if (!(o.Username in hash)) {
            hash[o.Username] = r.push(o) - 1;
            return r;
        }
        if (r[hash[o.Username]].Time < o.Time) {
            r[hash[o.Username]] = o;
        }
        return r;
    }, []);
    
console.log(result);
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user_14476750

You can use .filter() with .some() within callback to check if any elements of array at greater indexes than current index within .filter() has current property value

const arr = [{"Username":"Patrick","Time":"08:01:32","Status":"log in"}
,{"Username":"Patrick","Time":"08:34:31","Status":"idle"}
,{"Username":"Patrick","Time":"08:52:10","Status":"meeting"}
,{"Username":"Patrick","Time":"10:07:52","Status":"daily tasks"}
,{"Username":"Patrick","Time":"12:00:11","Status":"lunch"}
,{"Username":"Mark","Time":"07:40:32","Status":"log in"}
,{"Username":"Mark","Time":"08:54:31","Status":"meeting"}
,{"Username":"Mark","Time":"09:52:10","Status":"idle"}
,{"Username":"Mark","Time":"10:07:52","Status":"daily tasks"}
,{"Username":"Mark","Time":"12:30:11","Status":"lunch"}];

let res = arr.filter(({Username:a}, i) =>
            !arr.some(({Username:b}, k) => k > i && a == b));
            
console.log(res);

user_28015590

In case someone is interested in getting the first ocurrence of each username there is a simple way to do it tweaking Nina's code a bit as follows:

var data = [{ Username: "Patrick", Time: "08:01:32", Status: "log in" }, { Username: "Patrick", Time: "08:34:31", Status: "idle" }, { Username: "Patrick", Time: "08:52:10", Status: "meeting" }, { Username: "Patrick", Time: "10:07:52", Status: "daily tasks" }, { Username: "Patrick", Time: "12:00:11", Status: "lunch" }, { Username: "Mark", Time: "07:40:32", Status: "log in" }, { Username: "Mark", Time: "08:54:31", Status: "meeting" }, { Username: "Mark", Time: "09:52:10", Status: "idle" }, { Username: "Mark", Time: "10:07:52", Status: "daily tasks" }, { Username: "Mark", Time: "12:30:11", Status: "lunch" }],
    hash = Object.create(null),
    result = data.reduce(function (r, o) {
        if (!(o.Username in hash)) {
            hash[o.Username] = r.push(o) - 1;
            return r;
        }
        if (r[hash[o.Username]].Time > o.Time) {
            r[hash[o.Username]] = o;
        }
        return r;
    }, []);

console.log(result);

Only change the if statement (if (r[hash[o.Username]].Time > o.Time)) and this will get you the results you need. I hope this helps someone out there.

user_38587570
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