Problem when converting NSString to NSNumber in iPhone

Question

Hey

I am having problem when converting string (YaxisData) to NSNumber. I have to return a NSNumber for Core-plot to get the graph done but its not working. Here's the sample code

-(NSNumber *)numberForPlot:(CPPlot *)plot field:(NSUInteger)fieldEnum recordIndex:(NSUInteger)index{

NSNumber *num = [NSNumber numberWithDouble:[[YaxisData objectAtIndex:index] doubleValue]];
return num;

}

num returns junk data such as -1 or 993494949494 but when I log the double value of number, it prints the correct value. I am not able to return this double value as the function signature requires only the NSNumber to be returned.

NSLog(@"Number: %f", [num doubleValue]);

I am stuck here and would really appreciate any help in this regard. Thanks!