• Create Account

Need scary sound effects or creepy audio loops for your next horror-themed game? Check out Highscore Vol.3 - The Horror Edition in our marketplace. 50 sounds and 10 loops for only \$9.99!

# Iterating in order over an unordered map

4 replies to this topic

### #1Servant of the Lord  Crossbones+   -  Reputation: 12472

Like
0Likes
Like

Posted 30 October 2013 - 08:00 PM

I have an std::unordered_map<MyStruct>. It's unordered for extra-fast lookups which is what will be needed most of the time. However, once, at startup, I'd like to iterate over it in order of MyStruct::myInt.

The container currently contains upwards of 2000 elements, and might reach as high as 5-10 thousand.

Is there some way I can iterate over it in an order other than its internal hashing order?

Edited by Servant of the Lord, 30 October 2013 - 08:05 PM.

It's perfectly fine to abbreviate my username to 'Servant' rather than copy+pasting it all the time.

All glory be to the Man at the right hand... On David's throne the King will reign, and the Government will rest upon His shoulders. All the earth will see the salvation of God.                                                                                                                                                       [Need free cloud storage? I personally like DropBox]

### #2Paradigm Shifter  Crossbones+   -  Reputation: 3963

Like
1Likes
Like

Posted 30 October 2013 - 08:03 PM

No.

If you know the keys used you can sort them and then look up the items in order.

You could put them in a map and iterate over them (and use the map to fill the unordered_map) then throw the map away.

"Most people think, great God will come from the sky, take away everything, and make everybody feel high" - Bob Marley

### #3Servant of the Lord  Crossbones+   -  Reputation: 12472

Like
0Likes
Like

Posted 30 October 2013 - 09:48 PM

Alright, thanks.

I'm now using a temporary map of references:

std::map<Key, std::reference_wrapper<Value>> sortedMap(std::begin(unsortedMap), std::end(unsortedMap));

for(const auto &pair : sortedMap)
{ ... }

It's perfectly fine to abbreviate my username to 'Servant' rather than copy+pasting it all the time.

All glory be to the Man at the right hand... On David's throne the King will reign, and the Government will rest upon His shoulders. All the earth will see the salvation of God.                                                                                                                                                       [Need free cloud storage? I personally like DropBox]

### #4Ryan_001  Prime Members   -  Reputation: 727

Like
3Likes
Like

Posted 30 October 2013 - 11:03 PM

I'm pretty sure boost::multi_index (http://www.boost.org/doc/libs/1_54_0/libs/multi_index/doc/index.html) can do what you're asking for.  You can set up a sequential index and an unordered index.

### #5wack  Members   -  Reputation: 785

Like
0Likes
Like

Posted 03 November 2013 - 04:54 PM

I'm pretty sure boost::multi_index (http://www.boost.org/doc/libs/1_54_0/libs/multi_index/doc/index.html) can do what you're asking for.  You can set up a sequential index and an unordered index.

Thanks for the tip about multi_index. Just used it to clean up a monstrosity with multiple containers that I created a while back.

Boost contains so much, it's tricky to really get an overview of the stuff you acually need sometimes...

PARTNERS