Question

I have an NSMutableDictionary that possibly contains more than twenty objects.
If it contains more than 20 objects, how should I remove the oldest entries until there is only 20 left?

For example, NSMutableDictionary with objects:

a = "-1640531535";
b = 1013904226;
c = "-626627309";
d = 2027808452;
e = 387276917;
f = "-1253254618";
g = 1401181143;
h = "-239350392";
i = "-1879881927";

With max number of objects: 5, should become:

a = "-1640531535";
b = 1013904226;
c = "-626627309";
d = 2027808452;
e = 387276917;

Thank you.

Answer 1

If all you’re looking for is 20 elements, I’d try something like:

NSMutableDictionary* newDict = [NSMutableDictionary new];
int                  count = 0;

for (id theKey in oldDict)
{
    [newDict setObject:[oldDict getObjectForKey:theKey] forKey:theKey];

    if (++count == 20)
        break;
}

[oldDict release];
oldDict = newDict;

The idea being that you copy the elements of the first 20 keys you find into a new dictionary, then replace the old one with the new one. If you want to iterate the dictionary via other means you could do that too, but the code above wouldn’t have to change much.