Question 266314 in Javascript Question posted in
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Javascript – filter one array of objects using another array of objects

I want to filter one array of objects using another array of object, like in the following code snippet:

const entries =  [{
      "id" : 1,
      "name" : "Entry 1",
      "topics" : [ {
        "id" : 101,
        "name" : "topic 1.1"
      }, {
        "id" : 102,
        "name" : "topic 1.2"
      }, {
        "id" : 103,
        "name" : "topic 1.3"
      }]
    }, {
      "id" : 2,
      "name" : "Entry 2",
      "topics" : [ {
        "id" : 201,
        "name" : "topic 2.1"
      }, {
        "id" : 202,
        "name" : "topic 2.2"
      }, {
        "id" : 203,
        "name" : "topic 2.3"
      }]
    }, {
      "id" : 3,
      "name" : "Entry 3",
      "topics" : [ {
        "id" : 25,
        "name" : "topic 3.1"
      }, {
        "id" : 26,
        "name" : "topic 3.2"
      } ]
    }];
    
 const filters = [{
      "id" : 1,
      "topics" : [ {
        "id" : 101,
      }, {
        "id" : 102,
      }]
    }, {
      "id" : 2,
      "topics" : []
    }];

const result =  entries.filter(
        ({ id, topics }) =>
          filters.some(
            ({ id: idFromFilteres, topics: topicsFromFilters }) => idFromFilteres === id && topicsFromFilters.length > 0,
          ) ,
      ).map(({ id, topics, ...rest }) => ({
        id,
        topics: topics?.filter(({ id: topicId }) =>
          filters.some(
            ({ topics: topicsFromFilter }) =>
              topicsFromFilter.some(
                ({ id: topicIdFromFilter }) => topicIdFromFilter === topicId,
              ),
          ),
        ),
        ...rest
      }));
      
  console.log(result);

The code is working fine, but I don’t like how I’m iterating again the entries array to filter the topics, notice that also entries with empty topics get filtered as well.

Is there a way to filter this array using one single iteration?

Tags:

2

Answers


  1. 0

    How about filter and map functions:

    // to map filter topics to entry IDs.
const map = new Map(filters.map((filter) => [filter.id, filter.topics.map((topic) => topic.id)]));

const result = entries.filter((entry) => {
  const topics = map.get(entry.id);
  return topics && topics.length > 0;
}).map((entry) => {
  const topics = map.get(entry.id);
  entry.topics = entry.topics.filter((topic) => topics.includes(topic.id));
  return entry;
});
    • filter: remove entries without matching filter topics
    • map: filter topics for the remaining entries
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  2. 0

    You can use reduce() to to iterate over the entries array and filter it based on the filters array.

    Example

       const result = entries.reduce((filteredEntries, entry) => {
      const matchingFilter = filters.find(filter => filter.id === entry.id);
    
      if (matchingFilter) {
        const filteredTopics = entry.topics.filter(topic =>
          matchingFilter.topics.some(filterTopic => filterTopic.id === topic.id)
        );
    
        if (filteredTopics.length > 0) {
          filteredEntries.push({ ...entry, topics: filteredTopics });
        }
      }
    
      return filteredEntries;
    }, []);
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