On Mar 13, 2008, at 6:24 PM, Jens Alfke wrote:
You don't necessarily need to sort all of it at once. You just need
to find the first few items, to display in your table view. If the
user scrolls past those, you need to find more. You can do this by
streaming the data from a file, keeping only the number of items
you need in memory at once. This sort of task is typically called
"external sorting", and Knuth and most other algorithm texts talk
about it.
Hmm, I'm not displaying in a table. I am simply trying to sort a
large file for later use (so that later it can be brought up bits at
a time in a meaningful order). But I get the point, I may need to try
doing an external sort.
But that said, the sort you're doing shouldn't freeze or crash, not
unless you eat up your processes' entire address space or use up so
much VM that the system starts to thrash. You'll have to provide
more details of what's happening.
It sounds like my program shouldn't be freezing in the first place,
since my files are not THAT big. Here are the details.
@interface GenericRecord : NSObject <NSCopying>
{
NSMutableArray *record;
... plus a couple ivars not used for the sort
}
@interface GenericTable : NSObject <NSCoding>
{
NSMutableArray *records; // the records of data
... plus a couple ivars not used for the sort
}
// IN GenericTable implementation
- (void) sortRecordsByField: (int) fieldNum;
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; //
experimental! initially ran without it...
NSArray *sortedArray;
void *i;
i = (void *) &fieldNum;
sortedArray = [records sortedArrayUsingFunction: sortGenericRecord
context: i]; // FROZE AFTER 20 MIN OF EXECUTION HERE
// [self setRecords: [NSArray arrayWithArray: sortedArray]];
[self setRecords: [NSMutableArray arrayWithArray: sortedArray]]; //
DID NOT GET THIS FAR....
[pool release];
}
// in GenericRecord implementation
int sortGenericRecord (GenericRecord *rec1, GenericRecord *rec2, void
*fieldNum)
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
int *columnPtr = (int *) fieldNum;
int column = *columnPtr;
NSString *rec1Field = [rec1 fieldAtIndex: column]; // no new alloc,
just ptr assignment
NSString *rec2Field = [rec2 fieldAtIndex: column]; // ibid => how
can I make smaller footprint?
NSLog(@"REC 1: %@ REC 2: [EMAIL PROTECTED]", rec1Field,
rec2Field);
return [rec1Field compare: rec2Field];
[pool release]; // I'm not sure whether the pool helps since no
convenience constructors, but tried anyway.
}
An alternative method passes an array via the void pointer so that I
can have primary, secondary... n'ary sort fields. Not shown, since I
at this point I'm not even past first base. Thanks.
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