Question

I have 2 NSArray (Mutable, actually) that I am trying to convert to a C-style double array for a c routine i am passing them to.

Here is my Objective-C routine:

NSMutableDictionary *childDictionary = [myParentDictionary objectForKey:resort_code];

latitudeArray = [childDictionary objectForKey:@"lat"];
longitudeArray = [childDictionary objectForKey:@"lon"];

int nvert = [latitudeArray count];
double laArray[nvert];
double loArray[nvert];

for(int i=0; i<nvert; i++) {
    double dLat = [[latitudeArray objectAtIndex:i]doubleValue];
    double dLon = [[longitudeArray objectAtIndex:i]doubleValue];
    laArray[i] = dLat;
    loArray[i] = dLon;
}

This takes upwards of 3-8 seconds on the 3G iPhone (instantaneous on the simulator — yet another reason to test on the device )

is there faster way? I have to end up with laArray[i] and loArray[i] as c-style arrays of doubles.

(to expand on the question for the benefit of a commenter):
Each array consists of @”38.448745″ (lat) and @”-122.9847684″ (lon) style content. I do this cos to be pushed onto an NSArray, the lat and lon need to be objects. I simply used:

[latitudeArray addObject:[NSString stringWithFormat: @"%.10f",dlat]];
[longitudeArray addObject:[NSString stringWithFormat: @"%.10f",dlon]];

I suppose I could change that to:

[latitudeArray addObject:[NSNumber numberWithDouble: @"%.10f",dlat]];
[longitudeArray addObject:[NSNumber numberWithDouble: @"%.10f",dlon]];

…which may reduce the conversion time of

double dLat = [[latitudeArray objectAtIndex:i]doubleValue];

but wouldn’t I still need that exact line to convert from NSString to double? It just may work faster?

thx

Answer 1

dlat is a double, right?

So instead of:

[latitudeArray addObject:[NSString stringWithFormat: @"%.10f",dlat]];

Do:

[latitudeArray addObject:[NSNumber numberWithDouble:dlat]];

They both respond to doubleValue but the NSNumber should not have to do any string parsing since it’s stored as a numeric value already. And you never have to go to a string at all.