How can I get all values for specific key from each NSDictionary in an NSArray? [duplicate]

问题

I have an array which contains dictionary objects. In each dictionary the key are common. Now I want to get all the values of that key. I have got these values with iteration, but I am looking for some straight forward way or a default method which does this job.

Can you please help me to get one default method which serves the purpose? Thanks.

Data Structure is like this:

<array>
    <dict>
        <key>Match</key>
        <string>Football</string>
        <key>Stadium</key>
        <string>XXXXX</string>
    </dict>
    <dict>
        <key>Match</key>
        <string>HOCKY</string>
        <key>Stadium</key>
        <string>XXXXX</string>
    </dict>
 </array>

I am doing this now:

NSMutableArray * matches = [[NSMutableArray alloc] init];
        for (int i = 0; i< myArray.count; i++){
            [matches insertObject:[[myArray objectAtIndex:i] objectForKey:@"Match"] atIndex:i];
        }
        [matchDataArray addObjectsFromArray:matches];

It gives me correct answer. But I don't want to do this iteration. I want a method which will return me all values of "Match" key from all indexes of array and save in another array at once. newly created array will have only the values of Match key from all indexes of array.

Is this possible??

回答1:

There's a neat trick with key-value coding that does it:

NSArray *matches = [myArray valueForKey: @"Match"];

Here is an example in action:

NSArray *anArray = @[
                      @{@"aWord" : @"I"},
                      @{@"aWord" : @"have"},
                      @{@"aWord" : @"an"},
                      @{@"aWord" : @"array"},
                      @{@"aWord" : @"which"},
                      @{@"aWord" : @"contains"},
                      @{@"aWord" : @"dictionary"},
                      @{@"aWord" : @"objects."},
                      @{@"aWord" : @"Etc."},
                      ];

NSArray *aWordArray = [anArray valueForKey:@"aWord"];

After this last line, aWordArray will contain the words in the same order as in the original array of dictionaries.

来源：https://stackoverflow.com/questions/15018037/how-can-i-get-all-values-for-specific-key-from-each-nsdictionary-in-an-nsarray

标签

objective-c

nsarray

nsdictionary

key-value-coding