Using Angular's filter pipe to search within a nested array

Question

Using Angular's filter pipe to search within a nested array

We are attempting to implement an angular pipe for filtering a list of sub-items, with the goal of removing parent items if there are no child items present. Here is the HTML code snippet we are using:

   <div class="row border-bottom item" *ngFor="let item of pageContent | filter: searchText; let i = index">
      <div class="col-6">{{item.name}}</div>
      <div class="col-6">
        <ul>
          <li *ngFor="let link of item.content">
            {{link.content}}
          </li>
        </ul>
      </div>
    </div>

This is how our pipe is defined:

export class FilterPipe implements PipeTransform {
transform(items: AllContent[], searchText: string): AllContent[] {

if (!items) return [];
if (!searchText) return items;


return items.filter(item => {
  item.content.filter(c => c.content.toLowerCase().includes(searchText.toLowerCase()))
})

We have been unable to successfully filter out the child items. We have also attempted the following approach:

return items.foreach(item => {
item.content.filter(c => c.content.toLowerCase().includes(searchText.toLowerCase()))
})

Is there something that we might be overlooking or missing in our implementation?

javascript angular typescript

Answer 1

Answer №1

The filter method is missing a crucial return statement and you must remember to include .length:

return items.filter(item => {
  // make sure to add the return keyword and append .length at the end
  return item.content.filter(c => c.content.toLowerCase().includes(searchText.toLowerCase())).length
})

For one-liners, there's no need for the return keyword, but when splitting into multiple lines with curly braces {...}, you must explicitly return the items. This also applies to array.map().

Note @Adam Jenkins' comment: The condition in an array.filter() method should evaluate to either true or false (or something truthy/falsey). The inner nested .filter() always returns an array which is truthy, causing the outer .filter() to return all items. To fix this, appending .length after the nested filter() will ensure it evaluates correctly. A better alternative could be utilizing .some() for improved performance.

If filtering both the pageItem and its content, consider the following approach (assuming pipeline resets items on filter):

items = items.filter(item => {
    item.content = item.content.filter(c => c.content.includes(searchText))
    return item.content.length ? true : false
})
return items

Also worth noting, based on current structure, it seems like an item contains a property named content which itself has a property of content. Confirm if this aligns with your intended design.

Answer 2

The filter method is missing a crucial return statement and you must remember to include .length:

return items.filter(item => {
  // make sure to add the return keyword and append .length at the end
  return item.content.filter(c => c.content.toLowerCase().includes(searchText.toLowerCase())).length
})

For one-liners, there's no need for the return keyword, but when splitting into multiple lines with curly braces {...}, you must explicitly return the items. This also applies to array.map().

Note @Adam Jenkins' comment: The condition in an array.filter() method should evaluate to either true or false (or something truthy/falsey). The inner nested .filter() always returns an array which is truthy, causing the outer .filter() to return all items. To fix this, appending .length after the nested filter() will ensure it evaluates correctly. A better alternative could be utilizing .some() for improved performance.

If filtering both the pageItem and its content, consider the following approach (assuming pipeline resets items on filter):

items = items.filter(item => {
    item.content = item.content.filter(c => c.content.includes(searchText))
    return item.content.length ? true : false
})
return items

Also worth noting, based on current structure, it seems like an item contains a property named content which itself has a property of content. Confirm if this aligns with your intended design.

Answer 3

Answer №2

The issue stems from how you've implemented the filter function. When using the filter function, a new array is generated with elements that meet the criteria set by the provided function. However, in your current setup, you are applying the filter to the parent item without returning the outcome of this operation.

Below is the revised version of your custom pipe:

import { Pipe, PipeTransform } from '@angular/core';
@Pipe({
    name: 'filter'
})
export class FilterPipe implements PipeTransform {
    transform(items: AllContent[], searchText: string): AllContent[] {
        if (!items) return [];
        if (!searchText) return items;
        return items.filter(item => {
            item.content = item.content.filter(c => c.content.toLowerCase().includes(searchText.toLowerCase()));
            return item.content.length > 0; // Exclude parent items without matching sub-items
        });
    }
}

Answer 4

The issue stems from how you've implemented the filter function. When using the filter function, a new array is generated with elements that meet the criteria set by the provided function. However, in your current setup, you are applying the filter to the parent item without returning the outcome of this operation.

Below is the revised version of your custom pipe:

import { Pipe, PipeTransform } from '@angular/core';
@Pipe({
    name: 'filter'
})
export class FilterPipe implements PipeTransform {
    transform(items: AllContent[], searchText: string): AllContent[] {
        if (!items) return [];
        if (!searchText) return items;
        return items.filter(item => {
            item.content = item.content.filter(c => c.content.toLowerCase().includes(searchText.toLowerCase()));
            return item.content.length > 0; // Exclude parent items without matching sub-items
        });
    }
}

Answer 5

Answer №3

Utilize the map function to filter out elements in an array and create a new array of filtered items.

export class FilterPipe implements PipeTransform {
  transform(items: AllContent[], searchText: string): AllContent[] {
    if (!items) return [];
    if (!searchText) return items;

    return items
      .map(item => { // Use map to transform each item
        return {
          ...item,
          content: item.content.filter(c => c.content.toLowerCase().includes(searchText.toLowerCase()))
        };
      })
      .filter(item => item.content.length > 0); // Use filter to remove items with no content
  }
}

Answer 6

Utilize the map function to filter out elements in an array and create a new array of filtered items.

export class FilterPipe implements PipeTransform {
  transform(items: AllContent[], searchText: string): AllContent[] {
    if (!items) return [];
    if (!searchText) return items;

    return items
      .map(item => { // Use map to transform each item
        return {
          ...item,
          content: item.content.filter(c => c.content.toLowerCase().includes(searchText.toLowerCase()))
        };
      })
      .filter(item => item.content.length > 0); // Use filter to remove items with no content
  }
}

Using Angular's filter pipe to search within a nested array

Answer №1

Answer №2

Answer №3

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