有没有更好的方法来循环遍历一个大数组来找到每个项目的数量？

Question

I have a JSON file with over 20k entries with the names of different tracks on Spotify. I was trying to count the number of times each song has been played by a specific artist.

function countInArray(array, what) {
    var count = 0;
    for (var i = 0; i < array.length; i++) {
        if (array[i] === what) {
            count++;
        }
    }
    nfPlays.push(count)
    return count;
}
nfSongs2 = []
nfSongs = []
nfPlays = []

for(var i = 0; i < dta.length; i++) {
  if(dta[i].artistName === "NF") {
    nfSongs.push(dta[i].trackName)
  }
}
for(var i = 0; i < dta.length; i++) {
  if(nfSongs2.indexOf(dta[i].trackName) === -1 && dta[i].artistName === "NF") {
    nfSongs2.push(dta[i].trackName)
  }
}

for(var i = 0; i < nfSongs2.length; i++) {
  console.log(`${nfSongs2[i]} has ${countInArray(nfSongs, nfSongs2[i])} plays`)

}

console.log(countInArray(nfSongs, "WHY"))

console.log(nfPlays)
console.log(nfSongs2)
console.log(nfSongs)

That's currently my code. Basically what it does is loop through the dta array and grab all the entries by NF (specifically the track names) which includes the duplicates, and then it does that again but this time, only grabbing unique names. Then I run countInArray on all the unique names of the tracks which will grab the number of plays and push it to the nfPlays array.

Not especially complicated and it does work. I was wondering if there is a better, shorter way of doing this.

Answer 1

I think you should try the filter method. For example:

function countInArray(array, what) {
    const foundItems = array.filter(value => value === what);
    nfPlays.push(foundItems.length)
    return foundItems.length;
}

Or

const foundTracks = dta.filter(track => track.artistName === "NF");

Background

Answer 2

You can use a Map which is presents a faster lookup than an array (indexOf)

 const dta = [ { trackName:'a', artistName:'NF' }, { trackName:'a', artistName:'NF' }, { trackName:'b', artistName:'NF' }, { trackName:'b', artistName:'other' }, ] const trackNameToCount = dta.reduce((m, track) => { if (track.artistName === 'NF') { const n = m.get(track.trackName) || 0 m.set(track.trackName, n+1) } return m }, new Map()) ;[...trackNameToCount.entries()].forEach(([name, count]) => { console.log(`${name} played ${count} times`) })

Answer 3

Hope I understand what you're doing. I'd suggest using the object type to handle duplicates. Something like this?

 dta = [ {trackName: "dog", artistName: "NF"}, {trackName: "dog", artistName: "mack"}, {trackName: "dog", artistName: "NF"}, {trackName: "cat", artistName: "fred"}, {trackName: "mouse", artistName: "NF"}, ] nfsongs = {} dta.forEach(item => { if (item.artistName==="NF") { if (item.trackName in nfsongs) { nfsongs[item.trackName]++; } else { nfsongs[item.trackName]=1; } } }) for (key in nfsongs) { console.log(`${key} has ${nfsongs[key]} plays`) }