CoreDataでcount関数を使う

gistfile1.txt

    //集計対象
    NSExpression *keyPathExpression = [NSExpression expressionForKeyPath:@"column1"];
    //集計関数countを指定
    NSExpression *countExpression = [NSExpression expressionForFunction:@"count:" arguments:@[keyPathExpression]];
    
    //集計式の対象（NSExpressionDescription ）
    NSExpressionDescription *expressionDescription = [[[NSExpressionDescription alloc] init] autorelease];
    [expressionDescription setName:@"count"];
    [expressionDescription setExpression:countExpression];
    [expressionDescription setExpressionResultType:NSInteger32AttributeType];
    
    [fetchRequest setPropertiesToGroupBy:@[column2]];
    [fetchRequest setPropertiesToFetch:@[column2, expressionDescription]];
    [fetchRequest setResultType:NSDictionaryResultType];