Comparing values within one JavaScript array of objects

Question

I have an array of objects like so:

[{ value: 40,
  username: 'Name 1',
  id: 'high'
},
{ value: 30,
  username: 'Name 2',
  id: 'low',
},
{ value: 60,
  username: 'Name 1',
  id: 'low',
},
{ value: 50,
  username: 'Name 2',
  id: 'high'
}]

I want to compare the objects with the same username key and return false where the object has the property id: low and its value is higher than any corresponding object with its id set to high.

So for this object false would be returned because the third object has the low for its id and it has a higher value than the corresponding object with the same username with high in its id.

Currently I'm filtering the array into two separate arrays like so.

    const higherTest = test.filter(item => item.id === 'high');
    const lowerTest = test.filter(item => item.id === 'low');

And then compare both using a nested for loop but this seems excessive and I am wondering if there is a cleaner way?

I like the two filter approach, maybe with an additional reduce on each to get the low value amongst the 'high' set and the high value amongst the 'low' set for subsequent comparison. And presumably grouped by username, if it's per user. — jarmod
– jarmod, Commented Mar 10, 2020 at 14:29
Can you provide an example of the output you're trying to achieve? — lucas
– lucas, Commented Mar 10, 2020 at 14:34
It would be helpful if you provide the output for the given array — Gowtham Koushik
– Gowtham Koushik, Commented Mar 10, 2020 at 14:35
The output I am looking for is a boolean value. For the above array false would be returned. — hezzag
– hezzag, Commented Mar 10, 2020 at 14:39

Nina Scholz · Accepted Answer · 2020-03-10 14:57:28Z

1

You could take a hash table for visited names and store the low and height value. If a pair is found check the values and return the result of the check.

This approach uses a short circuit and returns for the first found low > high condition.

var data = [{ value: 40, username: 'Name 1', id: 'high' }, { value: 30, username: 'Name 2', id: 'low' }, { value: 60, username: 'Name 1', id: 'low' }, { value: 50, username: 'Name 2', id: 'high' }],
    result = !data.some((m => ({ value, username, id }) => {
        const user = m[username] = m[username] || {};
        user[id] = value;
        return 'high' in user && 'low' in user && user.low > user.high;
    })({}));

console.log(result);

edited Mar 10, 2020 at 14:57

answered Mar 10, 2020 at 14:50

Nina Scholz

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