Generate an object tree given an object keyed by category hierarchy levels.

category-object-tree.js

const rawCategories = {
  'hierarchical_categories.level_1': {
    'Beverages': 349,
    'Coffee & Tea': 4,
    'Deli': 35
  },
  'hierarchical_categories.level_2': {
    'Beverages > Energy & Sports Drinks': 54,
    'Beverages > Juice & Nectars': 111,
    'Deli > Cheeses': 30
  },
  'hierarchical_categories.level_3': {
    'Beverages > Juice & Nectars > Orange Juice': 35,
    'Beverages > Juice & Nectars > Apple Juice': 35,
    'Deli > Cheeses > Specialty Cheeses': 3
  }
}

const desiredCategoryTree = {
  'Beverages': {
    count: 349,
    children: {
      'Energy & Sports Drinks': {
        count: 54,
        children: null
      },
      'Juices & Nectars': {
        count: 111,
        children: {
          'Orange Juice': {
            count: 35,
            children: null
          },
          'Apple Juice': {
            count: 35,
            children: null
          }
        }
      }
    }
  },
  'Coffee & Tea': {
    count: 4,
    children: null
  },
  'Deli': {
    count: 35,
    children: {
      'Cheeses': {
        count: 30,
        children: {
          'Specialty Cheeses': {
            count: 3,
            children: null
          }
        }
      }
    }
  }
}

const actualCategoryTree = generateCategoryTree(rawCategories)

expect(actualCategoryTree).toEqual(desiredCategoryTree)

function generateCategoryTree (categories = {}, level = 1) {
  return Object.keys(categories).reduce((next, category) => {
    const categoriesArray = category.split(' > ')
    const parent = categoriesArray[level - 1]
    const child = categoriesArray[level]
    const parentLineage = Object.keys(categories).find(key =>
      key.endsWith(parent)
    )
    const childLineage = Object.keys(categories).find(key =>
      key.endsWith(child)
    )

    if (!next[parent] || !child) {
      return {
        ...next,
        [parent]: {
          value: categories[child ? childLineage : parentLineage],
          children: null
        }
      }
    }

    const children = Object.keys(
      categories
    ).reduce((nextCategories, category) => {
      if (
        category.split(' > ').length > level &&
        category.startsWith(parentLineage)
      ) {
        nextCategories[category] = categories[category]
      }
      return nextCategories
    }, {})

    return {
      ...next,
      [parent]: {
        ...next[parent],
        children: generateCategoryTree(children, level + 1)
      }
    }
  }, {})
}