Filtering NSArray of NSDictionary Objects

Introduction

In this article, we will explore the process of filtering an NSArray of NSDictionary objects to remove duplicates based on a specific key-value pair. We will also delve into how to display only unique city names in a table view and show corresponding departments when a particular city is selected.

Background

An NSArray in Objective-C is a data structure that represents a collection of objects. A NSDictionary, on the other hand, is an unordered collection of key-value pairs where each key is unique and maps to a specific value. When working with arrays of dictionaries, it’s common to need to filter out duplicate entries based on a particular key.

Problem Statement

Given an array of dictionaries representing cities and their corresponding departments, we want to:

Remove duplicates of city names from the array.
Display only unique city names in the first table view.
When a particular city is selected, show its corresponding department in the next table view.

Example Data

Let’s consider an example array of dictionaries with city and department information for India:

Array values :
{
    city = uk;
    department = "Sales support";
},
{
    city = us;
    department = "Sales support";
},
{
    city = italy;
    department = "Sales support";
},
{
    city = india;
    department = "x";
},
{
    city = india;
    department = "y";
},
{
    city = india;
    department = "z";
}

Solution Overview

To solve this problem, we will use a combination of the following techniques:

Using an NSPredicate to filter out duplicate entries based on the city key.
Utilizing an NSArray’s sortedArrayUsingComparator method to remove duplicates while preserving order.
Implementing a didSelectRowAtIndexPath method to display departments corresponding to selected cities in a separate table view.

Step 1: Filtering Duplicates Using NSPredicate

To filter out duplicate entries based on the city key, we will use an NSPredicate. The predicate will be used to filter the responseArray and create a new array with only unique city names.

// Create a predicate that filters arrays containing specific values for "city"
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"city == %@", [cityArray objectAtIndex:indexPath.row]];

However, since we’re using sortedArrayUsingComparator, the code should be modified as follows:

// Create an array with unique city names by comparing each object to others using a custom comparator
NSArray *uniqueCities = [responseArray sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
    id value1 = [obj1 objectForKey:@"city"];
    id value2 = [obj2 objectForKey:@"city"];

    NSComparisonResult result = [value1 compare:value2];
    return (result == NSOrderedSame) ? NSOrderedSame : (result < 0) ? NSOrderedDescending : NSOrderedAscending;
}];

// Sort the array in ascending order to ensure predictable ordering
[uniqueCities sortUsingComparator:^NSComparisonResult(id obj1, id obj2) {
    // Sort based on city name
    id value1 = [obj1 objectForKey:@"city"];
    id value2 = [obj2 objectForKey:@"city"];

    NSComparisonResult result = [value1 compare:value2];
    return (result == NSOrderedSame) ? NSOrderedSame : (result < 0) ? NSOrderedDescending : NSOrderedAscending;
}];

Step 2: Loading First Table View with Unique City Names

To display only unique city names in the first table view, we will use an NSArray’s sortedArrayUsingComparator method.

// Sort the array of dictionaries to ensure predictable ordering and remove duplicates based on the "city" key
NSArray *uniqueCityArray = [responseArray sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
    // Compare objects using a custom comparator that checks if the city is the same
    id value1 = [obj1 objectForKey:@"city"];
    id value2 = [obj2 objectForKey:@"city"];

    NSComparisonResult result = [value1 compare:value2];
    return (result == NSOrderedSame) ? NSOrderedSame : (result < 0) ? NSOrderedDescending : NSOrderedAscending;
}];

// Load the first table view with unique city names
[self.tableView reloadData];

Step 3: Implementing didSelectRowAtIndexPath Method

To display departments corresponding to selected cities in a separate table view, we will implement a didSelectRowAtIndexPath method.

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    // Get the selected city from the indexPath
    NSString *selectedCity = [uniqueCityArray objectAtIndex:indexPath.row];

    // Create an array predicate for filtering responses based on the selected city
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"city == %@", selectedCity];

    // Filter the response array to get departments corresponding to the selected city
    NSArray *departments = [responseArray filteredArrayUsingPredicate:predicate];

    // Reload the second table view with the filtered departments
    [self.tableView2 reloadData];
}

Conclusion

In this article, we explored how to filter an NSArray of NSDictionary objects to remove duplicates based on a specific key-value pair. We also delved into how to display only unique city names in a table view and show corresponding departments when a particular city is selected.

By utilizing NSPredicate, NSArray’s sortedArrayUsingComparator method, and implementing a didSelectRowAtIndexPath method, we can efficiently manage data and provide a seamless user experience.

Last modified on 2024-03-13