如何计算一个巨大的项目列表

Question

I have a huge list of items about almost all the crops and these data is to be plotted using maps and charts. I would like to count the number of each crop, say how many times was cabbage planted. I use Firebase database to store the data and I retrieve it using this function below:

database = firebase.database()

var ref = database.ref('Planting-Calendar-Entries');
ref.on('value', gotData, errData);

function gotData(data){
    console.log(data.val())
    var veggie = data.val();
    var keys = Object.keys(veggie);
    console.log(keys);
    let counter = 0
    for (var i = 0; i < keys.length; i++){
      var k = keys[i];
      var Veg_planted = veggie[k].Veg_planted;
      var coordinates = veggie[k].coordinates;
      if (Veg_planted == 'Cabbage'){
        counter++;
      }
      // vegAll = Veg_planted.count()
      console.log(Veg_planted, coordinates)
    }
    console.log(counter)
  }
function errData(err){
    console.log('Error!');
    console.log(err)
}

This data I retrieve it from the database where it gets updated whenever someone submits their planting information. The code I used above will only apply if my list is small, but I have a list of about 170 items and it would be hard to write code to count each crop individually using something like let counter = 0, counter++ . Is there a way I could navigate around this?

Answer 1

Actually: the code to count the items is probably going to be the same, no matter how many items there are. The thing that is going to be a problem as you scale though is the amount of data that you have to retrieve that you're not displaying to the user.

Firebase does not support aggregation queries, and your approach only works for short lists of items. For a more scalable solution, you should store the actual count itself in the database too.

So:

• Have a blaCount property for each bla that exists.
• Increment/decrement the counter each time your write/remove a bla to/from the database.
• Now you can read only the counters, instead of having to read the individual items.

Answer 2

I'm assuming data.val() returns an array, not an object, and you're misusing Object.keys() on an array instead of just looping over the array itself. If that's true, then it sounds like you want to group by the Veg_planted key and count the groupings:

const counts = Object.values(veggie).reduce((counts, { Veg_planted }) => ({
    ...counts,
    [Veg_planted]: (counts[Veg_planted] || 0) + 1
}), {});

Usage:

const veggie = [{ Veg_planted: 'Cabbage' }, { Veg_planted: 'Cabbage' }, { Veg_planted: 'Corn' }];
// result of counts:
// {Cabbage: 2, Corn: 1}

Answer 3

Firestore would be better option. You can query based on the field value.

var plantingRef = db.collection("PlantingCalendarEntries");

var query = plantingRef.where("Veg_planted", "==", "Cabbage");

if you still want to stuck with realtime database.

1. Save Counters to database.
2. Or use cloud dunctions to count.