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Objective-C: Count the number of times an object occurs in an array? (12 answers)

Closed 8 years ago.

我需要一种办法,计算在任何特定可移动的阿雷拉发生物体的多少时间,然后将物体的索引归还给一枚可持久、可移动的阿雷。我尝试了这样做的两重方式,但必须加以说明。

So basically say I have an array containing 2,3,3,4,3,5,3 When searching for 3, it should give me both the number of times, 4, and a seperate array containing 1,2,4,6 (the indexes of the objects.

I saw the following code already here on the site, but cant work out how to modify it, can anyone help me?

int occurrences = 0;
for(NSString *string in array){
    occurrences += ([string isEqualToString:@"Apple"]?1:0); //certain object is @"Apple"
}

Answer 1

int occurrences = 0;
NSMutableArray *indices = [NSMutableArray array];
int i = 0;
for (i = 0; i < [array count]; i++) {
    NSString *obj = [array objectAtIndex:i];
    if ([obj isEqualToString:@"Apple"]) {
        occurrences++;
        [indices addObject:[NSNumber numberWithInt:i]];
    }
}

您也可以放弃对<代码>occurrences的跟踪,并做类似的事情。

int occurrences = [indices count];

。

Answer 2

  id thingYouAreLookingFor;

  NSIndexSet *result = [array indexesOfObjectsPassingTest:^BOOL(id obj, NSUInteger idx, BOOL *stop) {
    return [thingYouAreLookingFor equals: obj];
  }];

Answer 3

Easy way to do it if you don t mind time, it s a square time operation.

Keep a counter, recording how many elements from array1 has appeared in array2
for all element in array1, test if it exist in array2. If it exist, counter++, if not, continue.
return the counter.

使用<代码>[米表Array 含有目标:参数],以回收组合2 含有一个元素。

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