add if/else logic to JavaScript filter

Question

I have an array of objects which I filter with two different arrays. The array is a list of study classes that I want to filter by grade and subject.

I came up with this code:

this.schoolActivity.filter(x => {
    return (
        this.activeSubjects.includes(x.subject.toLowerCase()) &&
        this.activeGrades.includes(x.grade)
    );
});

which works fine but the issue here is that if there are no active subjects (subject to filter by) or the same for a grade, then nothing returns. Any idea how can I improve this filter by adding logic to the only filter by subject/grade if active ones exist?

What does "no active subjects" mean? x.subject is blank, or this.activeSubjects is empty? — T.J. Crowder
– T.J. Crowder, Commented Aug 21, 2019 at 7:27

CertainPerformance · Accepted Answer · 2019-08-21 07:29:41Z

5

Just add an || check to see if the length of the array in question is 0:

const { activeSubjects, activeGrades } = this;
this.schoolActivity.filter(x => {
  return (
    (activeSubjects.length === 0 || activeSubjects.includes(x.subject.toLowerCase())) &&
    (activeGrades.length === 0 || activeGrades.includes(x.grade))
  );
});

You could improve the computational complexity to O(n) rather than O(n^2) by using a couple of Sets instead of includes, but that probably doesn't matter.

edited Aug 21, 2019 at 7:29

answered Aug 21, 2019 at 7:26

CertainPerformance

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1 Comment

T.J. Crowder Over a year ago

I think you probably interpreted "no active subjects" better than I did.

T.J. Crowder · Accepted Answer · 2019-08-21 07:26:18Z

1

If I understand you right, you want to skip the filter on x.subject if it's blank. In which case:

this.schoolActivity.filter(x => {
    return (
      (!x.subject || this.activeSubjects.includes(x.subject.toLowerCase())) &&
      this.activeGrades.includes(x.grade)
    );
  });

The first condition will be true if x.subject is blank or it isn't blank and is on the list of active subjects.

answered Aug 21, 2019 at 7:26

T.J. Crowder

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Comments

Kumar · Accepted Answer · 2019-08-21 07:29:49Z

0

You can add logic to check if active Subjects & active grades exist

    this.schoolActivity.filter(x => {
        return (
            if(typeof this.activeSubjects !== 'undefined' && this.activeSubjects.length && typeof this.activeGrades !== 'undefined' && this.activeSubjects.length){
                this.activeSubjects.includes(x.subject.toLowerCase()) && this.activeGrades.includes(x.grade)
            }
        );
    });

answered Aug 21, 2019 at 7:29

Kumar

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Comments

Syed Afzal · Accepted Answer · 2019-08-21 07:39:38Z

-2

If I get your point then

this.schoolActivity.filter(x => {
    return (
      (this.activeSubjects && this.activeSubjects.includes(x.subject.toLowerCase())) &&
      (this.activeGrades && this.activeGrades.includes(x.grade))
    );
  });

answered Aug 21, 2019 at 7:39

Syed Afzal

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