How to count different values of an object inside an array

Question

In a database i have two colums: id and value. I want to check how many difrent id's there is in my result, how can i do that?

I have tried to think of an solution, but i haven't succeed more that countDifferentId(){// do some magic calculations}

result looks like this:

[ RowDataPacket {
    id: 76561198115203520,
    value: 73 },
  RowDataPacket {
    id: 76561198115029751,
    value: 73 }
  RowDataPacket {
    id: 76561198115702984,
    value: 73 },
  RowDataPacket {
    id: 76561198115203520,
    value: 73 } ]

So the result of countDifferentId() should be 3

McMuffinDK · Accepted Answer · 2018-02-07 14:45:10Z

3

If you want to do the job on javascript side, here you go:

const rowDataPackets = [
    {
        id: 76561198115203520,
        value: 73
    },
    {
        id: 76561198115029751,
        value: 73
    },
    {
        id: 76561198115702984,
        value: 73
    },
    {
        id: 76561198115203520,
        value: 73
    }
];


function countDifferentId(array){
    // Object with key=id to count unique ids and value is true (or whatever)
    const uniqueIds = array.reduce((acc, data) => Object.assign(acc, {[data.id]:true}) , {});
    // Number of unique ids is the number of keys
    return Object.keys(uniqueIds).length;
}

console.log(countDifferentId(rowDataPackets));

edited Feb 7, 2018 at 14:45

McMuffinDK

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answered Feb 7, 2018 at 4:36

RaphaMex

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3 Comments

McMuffinDK Over a year ago

This worked! Very compact and fast, just what i needed

McMuffinDK Over a year ago

Note: i changed const uniqueIds = rowDataPackets.reduce to const uniqueIds = array.reduce

RaphaMex Over a year ago

Good catch! happy it helps :)

Alex Brazh · Accepted Answer · 2018-02-07 01:36:50Z

2

Don't you want to do so in a group by query? There're lots of examples here. e.g.

https://www.w3resource.com/mysql/aggregate-functions-and-grouping/aggregate-functions-and-grouping-count-with-group-by.php

MySQL Query with count and group by

etc.

If you have only server request from API, you may want . to create a hash table like { id: count }

answered Feb 7, 2018 at 1:36

Alex Brazh

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7 Comments

McMuffinDK Over a year ago

I hoped for a JS solution as i think it is faster for me

RaphaMex Over a year ago

JS is not necessarily faster, it's often better share work between servers. Group by is a good option. If there's a lot of rows to fetch and you just want to count, even better do a select count(distinct id) from...

McMuffinDK Over a year ago

@RaphaMex the rows will not exceed 100 and i need to make a call every 1 second, is it still better?

RaphaMex Over a year ago

I made a pure JS solution, if you want to give it a try and compare. 100 rows every second, that's not a problem for either solution. I was just commenting in case you had thousands of rows, better relieve your network.

Brian Patterson Over a year ago

i agree that doing this at the query level is ideal, but sometimes its not a viable option depending on project dynamics.

|

Brian Patterson · Accepted Answer · 2018-02-07 02:01:01Z

1

function grabs all values from one array column and returns as an array.

then for loop uses an array to store counted values, checking the array each time to ensure values counted only once.

function getCol(myarray, col){ 
    var column = []; 
    for(var i=0; i<myarray.length; i++){ 
        column.push(myarray[i][col]); 
    } 
    return column; 
    }

    cols = getCol(result, 'id');
    var count = 0;
    var used = [];
    for(var i = 0; i<cols.length;i++){
         if(!used.indexOf(cols[i])){
               used.push(cols[i]);
               count++;
         }
     }

edited Feb 7, 2018 at 2:01

answered Feb 7, 2018 at 1:38

Brian Patterson

1,6252 gold badges16 silver badges31 bronze badges

9 Comments

McMuffinDK Over a year ago

Can you please explain your answer?

Brian Patterson Over a year ago

crappy stack app posted this twice ugh

McMuffinDK Over a year ago

Indeed it is crap

McMuffinDK Over a year ago

If i wanted to call getCol() how would i parse the MySQL result into the function?

Brian Patterson Over a year ago

getCol(result,'id');

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