Frequency

Rather than keeping track of values, maybe you want to keep track of the number of times an event occurs, without caring much about the data itself.

In ixfx, we can use Trackers.frequency . Note that the object is mutable.

Adding and clearing

Run
import { Trackers } from "https://unpkg.com/ixfx/dist/bundle.js"

// Create an instance
const freq = Trackers.frequency();

// Add data, here several at once
freq.add(`apples`, `oranges`, `apples`, `pears`, `pears`);

// Get frequencies as an array
const t = freq.toArray(); // [ ["apples", 2], ["oranges",1],["pears",2] ]

Clear all data

freq.clear();

Calculating

Get the count of a specific group. Returns undefined if group is not found.

const f = freq.frequencyOf(`apples`); // 2

It can be useful to work with the relative frequency rather than the absolute amount. For example, apples appears 40% of the time:

const rel = freq.relativeFrequencyOf(`apples`); // 0.4

To find the smallest, largest, average frequencies as well as the total frequency (ie. how many things have been added):

// Returns {min, max, avg, total}
const mma = freq.minMaxAvg();
console.log(`Average frequency is ${mma.avg}`);

Iterating

You can get the data as an array and iterate:

const data = freq.entries(); // freq.toArray() gives same result
for (const [group, count] of data) {
  console.log(`${group} has a count of ${count}`); // apples has a count of 2...
}

Custom objects

To keep track of objects, provide a function that creates a string for the items you’re adding. This allows you to group by different fields, or some combination of fields.

In the below example, cars are grouped by their make:

Run
import { frequency } from "https://unpkg.com/ixfx/dist/trackers.js"

// Two cars
const cars = [
  {
    make: `Toyota`,
    model: `Corolla`,
    year: 1980
  },
  {
    make: `Honda`,
    model: `Civic`,
    year: 1985
  }
]

// Count cars by make
const freq = frequency(car => car.make);

// Add array of cars
freq.add(...cars);

// Count a group
freq.frequencyOf(`Toyota`); // 1

// Or by object, which uses the same stringify function
freq.frequencyOf(cars[1]); // 1

Demo

The below demo calculates frequency distribution of letters in a string.