Removing the keys in a map in a loop context would reduce the map size?

Question

I am trying to reduce the searching area inside a loop once i have satisfied some condition. That means i want to reduce the size of the map by removing the keys in it. Those keys and the related data have already been processed so i am thinking it is unnecessary to having them in the map and try to avoid going through them once again inside the loop. Is that possible? Please suggest.

Here, mpSFDCSAP is a map.

            for(SAP_Customer_Master__c s: mpSFDCSAP.values()) {
                String[] strArr2 = s.Customer_Name__c.split(' ');
                String strCustName = '';
                if((strArr2[0].length()==1 && strArr2[0].StartsWith('A')) || (strArr2[0].length()==3 && strArr2[0].StartsWith('The'))) {
                    strCustName = strArr2[1].toLowerCase();
                }else{
                    strCustName = strArr2[0].toLowerCase();
                }

                if(strCustName.startsWith(strAccName)) {
                    lstSAPCustMast.add(s);
                }       
             mpSFDCSAP.remove(some keys); 
            //I am thinking the above line would reduce my map size 
            //and improve the performance of the loop by 
           //preventing to lookup the visited records once again.
           //Does it work inside the context of a loop, because loop variable is the map itself
            } 

Answer 1

You must not modify a collection of any sort while it is an iterator loop. This may cause erratic or fatal behavior. That includes adding elements to the collection, removing them, or re-ordering them via sort.

What you can do, however, is clone the map's keys, and then iterate over those:

for(String key:myMap.keySet().clone()) {
    // myMap.get(key), process that value
    myMap.remove(key);
}

You can use this technique when you need the heap space freed as soon as possible.

Answer 2

Reducing key size for performance reasons won't help, as when working with a map, one doesn't ever iterate over the keyset - you just do a Map.get(key). In your case, you're iterating over all the values, which means I have to ask:

Why are you using a map and iterating over values? If you only need the values, then just make a list and don't even have a map.

It's an interesting idea, but I don't think it will work, and it's unnecessary. I don't see why you would need to prevent looking in visited records, as you're just iterating through the list once.