How to retrieve distinct items from Firebase database?

Question

I'm writing an Android app and I need to retrieve all the distinct values of the field 'brand' from the Firebase Database given below. How do I do that?

Answer 1

I initiated Firebase functions and wrote a TypeScript function

  db.collection('assignments').orderBy('subject')
  .get().then(value => {
   var subjects: string[] = [];
   value.docs.forEach(doc =>{
     const thisSubject = doc.data()['subject'];
     console.log(thisSubject);
  //here's where the filtering is
     if (!subjects.includes(thisSubject)){
                 subjects += thisSubject;
     };
 }
);

That will at least get you to the array, then you can return the array to your Android app (or whatever you've initialized on Firebase).

Answer 2

If you are a Kotlin user, You may do it

fun <T> Array<out T>.distinct(): List<T>
fun ByteArray.distinct(): List<Byte>
fun ShortArray.distinct(): List<Short>
fun IntArray.distinct(): List<Int>
fun LongArray.distinct(): List<Long>
fun FloatArray.distinct(): List<Float>
fun DoubleArray.distinct(): List<Double>
fun BooleanArray.distinct(): List<Boolean>
fun CharArray.distinct(): List<Char>

reference : https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/distinct.html