Algorand NFT - Rarity Scores

rarity-scores.js

const rarityScore = getTraitRarityScore(nft, allNfts);

// https://medium.com/@nfthelperbot/understanding-nft-rarity-calculation-c724518efd63
// rarityScore = 1 ÷ ([Number of Items With That Trait Value] / [Total Number of Items in Collection])
function getTraitRarityScore(nft, allNfts) {
  if (!nft?.metadata?.properties || Object.keys(nft.metadata.properties).length === 0) return 0;

  const total = allNfts.length;
  const traitFrequencies = getTraitFrequencies(allNfts);
  const rarityScore = Object.entries(nft.metadata.properties).reduce((acc, [trait, value]) => {
    const traitFrequency = traitFrequencies[`${trait}:${value}`];
    const rarity = 1 / (traitFrequency / total);
    return acc + rarity;
  }, 0);
  return rarityScore;
}

function getTraitFrequencies(allNfts) {
  const formattedNfts = allNfts.map((nft) => {
    if (!nft.metadata?.properties) {
      return {};
    }
    return {
      ...nft.metadata?.properties,
    };
  });

  const traitFrequencies = {};
  formattedNfts.forEach((nft) => {
    Object.entries(nft).forEach(([trait, value]) => {
      traitFrequencies[`${trait}:${value}`] = (traitFrequencies[`${trait}:${value}`] || 0) + 1;
    });
  });
  return traitFrequencies;
}