Ngram creation with probabilities

ngrams.js

function n_grams(tokens,n = 2,sep = ' ',epoch = 3) {
    var ngrams = [];
    for (let j=0; j < epoch; j++) {
      //remove first token
      if (j!=0){tokens.shift();}
      for (var i = 0; i < tokens.length -n; i+=n) {
  
        let ng1 = tokens.slice(i, i+n).join(sep);
        let ng2 = tokens.slice(i+n, i+n+n).join(sep);
        let ngram = [ng1.replace(/\s?(START|END)\s?/gm,'')/*.trim()*/, ng2.replace(/\s?(START|END)\s?/gm,'')/*.trim()*/];
        //   /!\ pas de trim() à cause des tokens sur chars
       // console.log(`${i} : ${tokens[i]}`);
        if (tokens[i]  === 'START') {
          ngrams.push(["START", ng1.replace(/(START|END)\s?/g, '')]);
          ngrams.push([ng1.replace(/(START|END)\s?/g, ''),ng2]);
        } else if (tokens[i+n] === 'START') { // i+n+n est donc START
          ngrams.push([ng1, "END"]);
          //ngrams.push(["START", ng1.replace(/START\s?/g, '')]);
        
        } else if (i === tokens.length) {
          ngrams.push([ng1, "END"]);
        } else {
         // console.log(`On peut pusher i: ${i} / Token: ${tokens[i]} / Ngram: ${ngram}`);
          ngrams.push(ngram);
        }
      }
      
      console.log(`================================= Epoch ${j} : ${ngrams.length} ngrams`);
    }
      ngrams = [
        // count the number of times each ngram occurs
        ...ngrams
          .map(JSON.stringify)
          .reduce((acc, v) => acc.set(v, (acc.get(v) || 0) + 1), new Map())
          .entries(),
      ].map(([k, v]) => JSON.parse(k).concat(v)).sort(function (a, b) {
        return b[2] - a[2];
      });
      //groups
      let groups = ngrams.reduce((acc, cur) => {
        if (!acc[cur[0]]) {
          acc[cur[0]] = [];
        }
        acc[cur[0]].push([cur[1],cur[2]]);
        return acc;
      },  {});
     // console.log('Groups: ',groups);
      //set probabilities
      Object.entries(groups).forEach(entry => {         
        const [key, value] = entry;
        //get sum and probabilities
        const sum = value.reduce((acc, cur) => acc + cur[1], 0);
        const probabilities = value.map(x => [x[0], x[1] / sum]);
        groups[key] = probabilities;
      });
      //console.log('Groups: ',groups);
    return groups; //Object.entries(groups);
    
  }