aka Fizzbuzz alternatives.

getColumnsForCategories(categories) {
    let categoriesCount = 0;
    for (var key in categories) {
      categoriesCount++;
    }

    let half = Math.floor(categoriesCount / 2);
    let remainder = categoriesCount % half;

    let categoriesLeftColumnLength = half + remainder;
    let categoriesRightColumnLength = half;

    let categoriesLeftColumn = new Set();
    for (let i = 0; i < categoriesLeftColumnLength; i++) {
      categoriesLeftColumn.add(categories[i]);
    }

    let categoriesRighttColumn = new Set();
    for (let i = categoriesLeftColumnLength; i < (categoriesLeftColumnLength + categoriesRightColumnLength); i++) {
      categoriesRighttColumn.add(categories[i]);
    }

    let categoriesColumns = new Map();
    categoriesColumns.set('left', categoriesLeftColumn);
    categoriesColumns.set('right', categoriesRighttColumn);

    return categoriesColumns;
   }

convertArrayOfDocumentariesToMap(documentaries, amountPerRow, amountTotal) {
    let cardDecks = new Map();

    let counter = 0;
    for (let i in documentaries) {
        if (+i === amountTotal) {
          break;
        }

        let documentary = documentaries[i];

        let cardDeck = cardDecks.get(counter);
        if (cardDeck === undefined || !cardDeck) {
          cardDeck = new Set();
        } 

        cardDeck.add(documentary);
        cardDecks.set(counter, cardDeck);

        if (+i != 0 && (+i + 1) % amountPerRow === 0) {
          counter++;
        }
    }

    return cardDecks;
   }