Javascript.Map

const individualDesignations = features.filter((feature) => {
      const duplicate = seen.has(feature.properties.Designatio);
      seen.add(feature.properties.Designatio);
      return !duplicate;
    });

    const allDesignations = individualDesignations.map((designation) => {
      return {
        name: designation.properties.Designatio,
        category: designation.properties.layer,
        isChecked: true,
      };
    });

    const designationNames = allDesignations.map(
      (designation) => designation.name
    );

    setDesignations(allDesignations);
    setCheckedDesignationLayers(designationNames);

    return allDesignations;
  };

const allSubcategoryDesignations = individualDesignations
    .filter((feat) => feat.properties.layer !== feat.properties.Designatio)
    .map((designation) => {
        // we're going through all the unique (by layer and designatio) designations here
        // for each one we want to find the correct subcategory data under the correct category
        // find out alternative names for it so that the Designatio becomes a proper subcategory.
        // we only want categories incuded that exist in our CATEGORIES constant
        const categoryInfo = CATEGORIES.find((category) => category.title === designation.properties.layer);
        if (categoryInfo !== undefined) {
            const category = designation.properties.layer;
            const subcategory = designation.properties.Designatio;
            // get all the possible subcategories for this category
            const subcategories = categoryInfo.hasOwnProperty('subcategories') ? categoryInfo.subcategories : [];
            const subcategoryInfo = subcategories.find((subcat) => subcat.title === subcategory)
            const isChecked = subcategoryInfo && subcategoryInfo.hasOwnProperty('isChecked') ? subcategoryInfo.isChecked : true;
            const order = subcategoryInfo && subcategoryInfo.hasOwnProperty('order') ? subcategoryInfo.order : -1;
            return {
                layer: designation.properties.layer,
                Designatio: designation.properties.Designatio,
                category: category,
                subcategory: subcategory,
                isChecked: isChecked,
                order: order,
                isTopLevel: false
            };
        }
        return {}
    }).filter(value => Object.keys(value).length !== 0);

setDesignations([...allSubcategoryDesignations, ...allTopLevelDesignations]);
setCheckedDesignations([...allSubcategoryDesignations, ...allTopLevelDesignations]);
return [...allSubcategoryDesignations, ...allTopLevelDesignations];