📘 C# Blog Series – Blog 36 **“C# LINQ — Collections को Filter, Sort, Group करने का सबसे Powerful तरीका

📘 C# Blog Series – Blog 36

**“C# LINQ — Collections को Filter, Sort, Group करने का सबसे Powerful तरीका

(Real-Life Example: GPS Devices को Battery, Status, Last-Update से Filter करना)”**

LINQ (Language Integrated Query) C# का superpower है।
इससे आप lists, arrays, dictionaries, database data—सबको
query style में process कर सकते हो।

क्यों useful है?

✔ Short code
✔ Fast
✔ Readable
✔ Zero loops
✔ SQL जैसा experience
✔ Perfect for GPS + API development

आज हम LINQ को real-life GPS server के examples के साथ सीखेंगे।

---

🟦 1. LINQ क्या है? (Simple Definition)

LINQ =
Collection को query करने का modern तरीके से लिखने का system।

Instead of:

foreach(...)
{
    if(...)
    {
        if(...)
        {
            list.Add(...);
        }
    }
}

You write:

var result = list.Where(x => x.Battery < 20);

Short + Clean.

---

🟢 2. Basic LINQ Syntax

list.Where(x => x.Speed > 50);
list.Select(x => x.IMEI);
list.OrderBy(x => x.Battery);
list.GroupBy(x => x.Status);

---

⭐ 3. Real GPS Model Example

class GPSDevice
{
    public string IMEI { get; set; }
    public int Battery { get; set; }
    public string Status { get; set; } // Online / Offline
    public DateTime LastUpdated { get; set; }
}

List:

List<GPSDevice> devices = GetDevices();

---

🌟 4. Filter — Low Battery Devices (Top Use Case)

var lowBattery = devices
                 .Where(d => d.Battery < 20)
                 .ToList();

अब आपके पास वह list है जो जल्दी alert भेजनी है।

---

⭐ 5. Filter — Offline Devices (Most common)

var offline = devices
              .Where(d => d.Status == "Offline")
              .ToList();

---

⭐ 6. Time-Based Filter — Last Updated 5 Min Ago

var outdated = devices
               .Where(d => DateTime.Now - d.LastUpdated > TimeSpan.FromMinutes(5))
               .ToList();

GPS server में यह सबसे ज़रूरी health check है।

---

🟠 7. LINQ OrderBy — Sort Devices by Battery

var sorted = devices
             .OrderBy(d => d.Battery)
             .ToList();

Low battery list generate करना आसान।

---

🔵 8. OrderByDescending — Highest Speed First

var fastest = devices
              .OrderByDescending(d => d.LastUpdated)
              .ToList();

---

🟣 9. Select — Only IMEI List

var imeis = devices
            .Select(d => d.IMEI)
            .ToList();

अब backend → frontend भेजने में lightweight data।

---

🔥 10. Select — Lightweight DTO

var dto = devices.Select(d => new 
{
    d.IMEI,
    d.Battery,
    d.Status
});

API responses में यही pattern use होता है।

---

⭐ 11. GroupBy — Status के आधार पर grouping

var grouped = devices
              .GroupBy(d => d.Status);

Usage:

foreach (var group in grouped)
{
    Console.WriteLine($"Status = {group.Key}, Count = {group.Count()}");
}

Result:

Online = 45
Offline = 12

Perfect for dashboard stats.

---

🔥 12. Max/Min — Real-Time Stats

Highest battery:

var maxBattery = devices.Max(d => d.Battery);

Lowest battery:

var minBattery = devices.Min(d => d.Battery);

---

🧠 13. FirstOrDefault — Find Specific IMEI

var dev = devices.FirstOrDefault(d => d.IMEI == "861128068064267");

---

📌 14. Any — Check if Any Offline Device?

bool anyOffline = devices.Any(d => d.Status == "Offline");

---

🎯 15. Count — कितने devices Online?

int onlineCount = devices.Count(d => d.Status == "Online");

---

⭐ 16. Complex Query — Multi Condition (Very Useful)

Low battery + Offline:

var list = devices
           .Where(d => d.Battery < 25 && d.Status == "Offline")
           .ToList();

---

🔥 17. LINQ + OrderBy + Take — Top 10 Least Updated Devices

var list = devices
           .OrderBy(d => d.LastUpdated)
           .Take(10)
           .ToList();

Perfect for server health monitoring.

---

🧪 18. LINQ Chaining (Professional Coding)

var risky = devices
    .Where(d => d.Battery < 30)
    .OrderBy(d => d.Battery)
    .Select(d => new { d.IMEI, d.Battery })
    .ToList();

4 line का logic → 1 chain में complete।

---

🔚 Conclusion

C# LINQ आपके system को बनाता है:

✔ Super clean
✔ Fast
✔ SQL-like
✔ Zero loops
✔ Perfect for GPS data
✔ Super easy filtering
✔ Real-time dashboards

Real-time GPS system में 90% data manipulation LINQ से ही होता है।