ReactiveStatisticsinAngular19

Reactive Statistics in Angular 19: Signals, Effects, and Smart Control Flow

Angular 19 brings us into a golden age of fine-grained reactivity with Signals, Effects, and a truly modern control flow syntax. In this guide, we’ll harness these tools to build a Reactive Statistics Analyzer that computes basic metrics (mean, variance, count) in real-time — just like a pro.

You'll see how to combine:

  • ✅ signal() and computed() for reactive data modeling
  • ✅ effect() for reactive side-effects (auto-logging, syncing, etc.)
  • ✅ Modern control flow with @for, @if, and @switch
  • ✅ Angular 19's cleanest patterns using standalone components and injectable services 
src/
  app/
    statistics/
       statistics.component.ts   
    services/
       statistics.service.ts

Use Case: Live Statistical Analyzer

Let’s build a calculator that:

  • Accepts numerical input
  • Dynamically updates count, mean, and variance
  • Logs all statistical events reactively using effect()

Step 1: The Statistics Service 

import { Injectable, signal, computed, effect } from '@angular/core';

@Injectable({ providedIn: 'root' })
export class StatisticsService {
  private values = signal<number[]>([]);

  count = computed(() => this.values().length);

  mean = computed(() => {
    const vals = this.values();
    return vals.length ? vals.reduce((a, b) => a + b, 0) / vals.length : 0;
  });

  variance = computed(() => {
    const vals = this.values();
    const mu = this.mean();
    return vals.length
      ? vals.reduce((acc, x) => acc + Math.pow(x - mu, 2), 0) / vals.length
      : 0;
  });

  constructor() {
    effect(() => {
      console.log(`Count: ${this.count()}, Mean: ${this.mean().toFixed(2)}, Variance: ${this.variance().toFixed(2)}`);
    });
  }

  add(value: number) {
    this.values.update(v => [...v, value]);
  }

  reset() {
    this.values.set([]);
  }

  get data() {
    return this.values;
  }
}

Step 2: UI Component with Control Flow 

import { Component } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { StatisticsService } from '../services/statistics.service';
import { CommonModule } from '@angular/common';

@Component({
  selector: 'app-statistics',
  standalone: true,
  imports: [FormsModule, CommonModule],
  template: `
  Reactive Stats Analyzer

  
  Add
  Reset

  @if (stats.count() > 0) {
    
      Count: {{ stats.count() }}
      Mean: {{ stats.mean().toFixed(2) }}
      Variance: {{ stats.variance().toFixed(2) }}
    
  } @else {
    No data yet — add some numbers!
  }

  History
  
    {{ val }}
  
`
})
export class StatisticsComponent {
  input = 0;
  constructor(public stats: StatisticsService){

  }
  submit(){
    this.stats.add(this.input);
    this.input = 0;
  }
  reset() {
    this.stats.reset();
  }

}

Summary

Concept Implementation
Reactive data signal([])
Derived data computed()
Logging effect() for automated tracking
Template flow @if, @for used for clean control flow

🧵 Final Thoughts

With Signals, Effects, and new control flow syntax, Angular 19 becomes a top-tier framework for reactive data visualization and state-driven UIs.

Build cleanly. Reactively. Mathematically.

Happy analyzing, and may your variance always stay low! ⚡