Display number of items from array of objects without duplicate

clck Published at Dev

clck

I'm learning javascript and I have some problems. I would like to iterate an array of objects but with a few "options":

don't display duplicate items.
display the number of items.

expected result :

received 1

missed 2

dialed 3

I know how to iterate a array of objects and use .length to display the quantity of each item but I don't know iterate + display quantity + remove duplicates... Can you help me ?

const calls = [
  {
    type: "missed",
    date: "xx-xx-xx"
  },
  {
    type: "received",
    date: "xx-xx-xx"
  },
  {
    type: "dialed",
    date: "xx-xx-xx"
  },
  {
    type: "missed",
    date: "xx-xx-xx"
  },
  {
    type: "dialed",
    date: "xx-xx-xx"
  },
  {
    type: "dialed",
    date: "xx-xx-xx"
  }
];

Alex L

A good way to group items is with reduce (it’s also flexible, so if you add another type it works no problem):

const calls = [{
    type: "missed",
    date: "xx-xx-xx"
  },
  {
    type: "received",
    date: "xx-xx-xx"
  },
  {
    type: "dialed",
    date: "xx-xx-xx"
  },
  {
    type: "missed",
    date: "xx-xx-xx"
  },
  {
    type: "dialed",
    date: "xx-xx-xx"
  },
  {
    type: "dialed",
    date: "xx-xx-xx"
  }
];

const output = calls.reduce((aggObj, item) => {
    if(!aggObj[item.type]){
        aggObj[item.type] = 0
    }
    aggObj[item.type] += 1;
    return aggObj;
}, {});
//output as object:
console.log(output);

//output as array:
const outArr = Object.entries(output);
console.log(outArr);

//output as strings:
outArr.forEach(([k,v]) => console.log(k,v));

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