Comparing values in two arrays

Question

I need some advice here. I have two arrays, with data that can be the same. I will compare these two row by row.

lastLoop [
  { position: '0', id: '5f862368df7d2700174c9df7' },
  { position: '1', id: '6111697148108400154a7cf9' },
  { position: '2', id: '610c1a8b132a880015c16a9d' },
  { position: '3', id: '5f8625e7df7d2700174c9df8' },
  { position: '4', id: '5fae7f6526ec3b0017710e60' },
  { position: '5', id: '61153dadd7db540015836e8e' },
  { position: '6', id: '5f849db0b0793b00177e2317' },
  { position: '7', id: '5fa85aba9c4a1900177e5cf9' },
  { position: '8', id: '6144d97107efcf001584706e' },
  { position: '9', id: '5e4463a395c832405e7effc5' }
]
newLoop [
  { position: '0', id: '5f862368df7d2700174c9df7' },
  { position: '1', id: '610c1a8b132a880015c16a9d' },
  { position: '2', id: '5fd7b30abb015f0017eda459' },
  { position: '3', id: '5fce234f9a61c100175f4b6d' },
  { position: '4', id: '5fca23930aa5e9001797a885' },
  { position: '5', id: '5f806a8b045fdf0017734fe8' },
  { position: '6', id: '5fc10c379378110017477dca' },
  { position: '7', id: '61153dadd7db540015836e8e' },
  { position: '8', id: '5f9b2c579050d2001785a253' },
  { position: '9', id: '5e4463a395c832405e7effc5' }
]

I want to make a leaderboard, if your position has changed up in the ladder, you get a green text, if it is the same, you get black text, if you have moved down the ladder you get a red text.

Any ideas?

If both arrays have the same length then a for-loop should do the job. — Core972
– Core972, Commented Oct 1, 2021 at 13:36
"Any ideas?" Yes, please try something yourself first. Then, if you cannot figure it out, post what you've tried and we can help you. Thanks. — Dexygen
– Dexygen, Commented Oct 1, 2021 at 13:48
Didn't ask for a solution, asked for advice in which direction, since I got stuck. I could have said what I tried and what not, for sure. Give me a break. — Mikael Blytung
– Mikael Blytung, Commented Oct 1, 2021 at 17:18

S.Visser · Accepted Answer · 2021-10-01 14:06:56Z

1

I would make a new object with an old_position key, based on this value you can decide what color you want to use.

const oldLeaderboard = [
  { position: '0', id: '5f862368df7d2700174c9df7' },
  { position: '1', id: '6111697148108400154a7cf9' },
  { position: '2', id: '610c1a8b132a880015c16a9d' },
  { position: '3', id: '5f8625e7df7d2700174c9df8' },
  { position: '5', id: '61153dadd7db540015836e8e' },
  { position: '4', id: '5fae7f6526ec3b0017710e60' },
  { position: '6', id: '5f849db0b0793b00177e2317' },
  { position: '7', id: '5fa85aba9c4a1900177e5cf9' },
  { position: '8', id: '6144d97107efcf001584706e' },
  { position: '9', id: '5e4463a395c832405e7effc5' }
]

const newLeaderboard = [
  { position: '0', id: '5f862368df7d2700174c9df7' },
  { position: '1', id: '610c1a8b132a880015c16a9d' },
  { position: '2', id: '5fd7b30abb015f0017eda459' },
  { position: '3', id: '5fce234f9a61c100175f4b6d' },
  { position: '4', id: '5fca23930aa5e9001797a885' },
  { position: '5', id: '5f806a8b045fdf0017734fe8' },
  { position: '6', id: '5fc10c379378110017477dca' },
  { position: '7', id: '61153dadd7db540015836e8e' },
  { position: '8', id: '5f9b2c579050d2001785a253' },
  { position: '9', id: '5e4463a395c832405e7effc5' }
]

const leaderBoard = newLeaderboard.map( item => ({
  posisiton: item.position,
  old_position: oldLeaderboard.filter(old => old.id === item.id)[0]?.position || null,
  id: item.id
}))

console.log(leaderBoard)

edited Oct 1, 2021 at 14:06

answered Oct 1, 2021 at 13:52

S.Visser

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2 Comments

Mikael Blytung Over a year ago

Thank you so much. I will figure it out with this logic.

NoOorZ24 Over a year ago

It's basically same as 2 nested for loops. Bad practice - poor performance

Dipu Kumar Sah · Accepted Answer · 2021-10-01 13:54:07Z

0

change the data-structure use HashMap (JSON) instead of array with id as key and position as value.

By doing you would reduce the total comparisons for an element and then simply compare the positions.

const newLoop =[
  { position: '0', id: '5f862368df7d2700174c9df7' },
  { position: '1', id: '610c1a8b132a880015c16a9d' },
  { position: '2', id: '5fd7b30abb015f0017eda459' },
  { position: '3', id: '5fce234f9a61c100175f4b6d' },
  { position: '4', id: '5fca23930aa5e9001797a885' },
  { position: '5', id: '5f806a8b045fdf0017734fe8' },
  { position: '6', id: '5fc10c379378110017477dca' },
  { position: '7', id: '61153dadd7db540015836e8e' },
  { position: '8', id: '5f9b2c579050d2001785a253' },
  { position: '9', id: '5e4463a395c832405e7effc5' }
]
const newLoopJSON={}
for (let i of newLoop){
  newLoopJSON[i.id]=i.position
}
const lastLoop= [
  { position: '0', id: '5f862368df7d2700174c9df7' },
  { position: '1', id: '6111697148108400154a7cf9' },
  { position: '2', id: '610c1a8b132a880015c16a9d' },
  { position: '3', id: '5f8625e7df7d2700174c9df8' },
  { position: '4', id: '5fae7f6526ec3b0017710e60' },
  { position: '5', id: '61153dadd7db540015836e8e' },
  { position: '6', id: '5f849db0b0793b00177e2317' },
  { position: '7', id: '5fa85aba9c4a1900177e5cf9' },
  { position: '8', id: '6144d97107efcf001584706e' },
  { position: '9', id: '5e4463a395c832405e7effc5' }
]

for(let {id,position} of lastLoop){
    if(newLoopJSON[id]){
        let new_POS=newLoopJSON[id]
        let difference=new_POS.id-id
        if(difference==0){ 
            // no change in new position and old position
            console.log("black")
        }
        else if(difference<0){
            // position increased
            console.log("green")
        }else{
            // position decreased
            console.log("red")
        }
        
    }
}

answered Oct 1, 2021 at 13:54

Dipu Kumar Sah

1

3 Comments

NoOorZ24 Over a year ago

What you call "JSON" is JavaScript pbject. JSON is format similar to to XML (similar in usage, in syntax not as much). Shouldn't teach someone terms you don't know yourself.

Dipu Kumar Sah Over a year ago

Bro, I guess you misinterpret I have not said JSON is a JS object. I called JSON a data-structure similar to HashMap with pair of key and value.

NoOorZ24 Over a year ago

But it's not a data structure. It's file format

Vasile Radeanu · Accepted Answer · 2021-10-01 13:59:07Z

// ...
const colorRules = [
  {
    color: "green",
    value: (oldP, newP) => +newP > +oldP
  },
  {
    color: "black",
    value: (oldP, newP) => +oldP === + newP
  },
  {
    color: "red",
    value: (oldP, newP) => +oldP > + newP
  },
]

const result = newLoop.map(player => {
  const oldHistory = lastLoop.filter(item => item.id === player.id);

  if (oldHistory.length) {
    const colorRulesMatch = colorRules.map((c) => ({
      ...c,
      value: c.value(oldHistory[0].position, player.position)
    }));

    const { color } = colorRulesMatch.filter(c => c.value)[0];

    return {
      ...player,
      color
    }
  } else {
    return {
      ...player,
      color: "black" // If player wasn't found in last loop
    }
  }
});

console.log(result);
// [
//   { position: '0', id: '5f862368df7d2700174c9df7', color: 'black' },
//   { position: '1', id: '610c1a8b132a880015c16a9d', color: 'red' },
//   { position: '2', id: '5fd7b30abb015f0017eda459', color: 'black' },
//   { position: '3', id: '5fce234f9a61c100175f4b6d', color: 'black' },
//   { position: '4', id: '5fca23930aa5e9001797a885', color: 'black' },
//   { position: '5', id: '5f806a8b045fdf0017734fe8', color: 'black' },
//   { position: '6', id: '5fc10c379378110017477dca', color: 'black' },
//   { position: '7', id: '61153dadd7db540015836e8e', color: 'green' },
//   { position: '8', id: '5f9b2c579050d2001785a253', color: 'black' },
//   { position: '9', id: '5e4463a395c832405e7effc5', color: 'black' }
// ]

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