Re: [Haskell-cafe] Trying to reduce memory costs of String duplicates

Hi Luke, thanks, this is some very good advice as I find many duplicates in the data I have to iterate over. However so far I'm unable to tell wether this actually works or not, I tried it a couple of times under different settings but it showed to difference in memory consumption. The same mem peeks as before. Do you have some code that where you could see a before and after? Günther Am 05.09.2009, 19:38 Uhr, schrieb Luke Palmer :

2009/9/5 Günther Schmidt :

...

Hi all,

I'm reading in a data of 216k records into a map of Key, Values Pairs, the values being strings.

As it happens out of 216k String values there really are only about 6.6k distinct string values, so I could save a lot of RAM if I was able to "insert" only actually *new* string values into the map and use references to (string) values that already are in memory instead.

Is there a container that would, if I wanted to insert an element, return a pair of either the previously inserted, equal value and the container unchanged, or the new, previously unknown value and the new container amended by that element?

I believe a memoization of the identity function will do what you want:

import qualified Data.MemoCombinators as Memo

share = Memo.list Memo.char id

Then pass any string through share to make/get a cached version.

You might want to limit the scope of share -- eg. put it in a where clause for the function where you're using it -- so that it doesn't eat memory for the lifetime of your program, only for when you need it.

Luke