Is there a way to iterate over a dictionary

Question

I know NSDictionaries as something where you need a key in order to get a value  But how can I iterate over all keys and values in a NSDictionary  so that I know what keys there are  and what values there are  I know there is something called a for-in-loop in JavaScript  Is there something similar in Objective-C

User · Answer

This is iteration using block approach       NSDictionary  dict       key1   1    key2   2    key3   3         dict enumerateKeysAndObjectsUsingBlock   id key  id obj  BOOL  stop            NSLog     - gt     key obj              Set stop to YES when you wanted to break the iteration            With autocompletion is very fast to set  and you do not have to worry about writing iteration envelope

User · Answer

The block approach avoids running the lookup algorithm for every key    dict enumerateKeysAndObjectsUsingBlock   id key  id value  BOOL  stop      NSLog        gt       key  value         Even though NSDictionary is implemented as a hashtable  which means that the cost of looking up an element is O 1    lookups still slow down your iteration by a constant factor   My measurements show that for a dictionary d of numbers      NSMutableDictionary  dict    NSMutableDictionary dictionary   for  int i   0  i  lt  5000000    i      NSNumber  value     i     dict value stringValue    value          summing up the numbers with the block approach        block int sum   0   dict enumerateKeysAndObjectsUsingBlock   NSString  key  NSNumber  value  BOOL  stop      sum    value intValue            rather than the loop approach      int sum   0  for  NSString  key in dict    sum     dict key  intValue         is about 40  faster   EDIT  The new SDK  6 1   appears to optimise loop iteration  so the loop approach is now about 20  faster than the block approach  at least for the simple case above

User · Answer

Yes  NSDictionary supports fast enumeration  With Objective-C 2 0  you can do this      To print out all key-value pairs in the NSDictionary myDict for id key in myDict      NSLog   key    value      key   myDict objectForKey key      The alternate method  which you have to use if you re targeting Mac OS X pre-10 5  but you can still use on 10 5 and iPhone  is to use an NSEnumerator   NSEnumerator  enumerator    myDict keyEnumerator   id key     extra parens to suppress warning about using   instead of    while  key    enumerator nextObject        NSLog   key    value      key   myDict objectForKey key

[ios] Is there a way to iterate over a dictionary?

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