ios NSPredicate to find nearest value in NSDictionary - ios

Question

I have an array of dictionaries like this:
(
{ key = 1, value = 40},
{ key = 4, value = 50},
{ key = 8, value = 60}
}
These are like this,
for >=1 item cost is 40,
for >=4 item cost is 50 and like wise.
I would like to get the value for 5, which in this case is 50.
The piece of code I have tried is:
NSMutableArray *wallpaperPriceArray = [[NSMutableArray alloc]init]; // Assuming this has all the dictionary values
float wallpaperPriceValue = 0;
int itemNumber = 0;
for (int i = 0; i<wallpaperPriceArray.count; i++) {
int check = 0;
if(itemNumber >= [[wallpaperPriceArray objectAtIndex:i] intValue])
{
wallpaperPriceValue = [[[wallpaperPriceArray objectAtIndex:i] objectForKey:#"value"] floatValue];
check++;
}
if(i + 1 <= wallpaperPriceArray.count)
{
if(itemNumber >= [[wallpaperPriceArray objectAtIndex:i+1] intValue] && itemNumber < [[wallpaperPriceArray objectAtIndex:i+1] intValue])
{
wallpaperPriceValue = [[[wallpaperPriceArray objectAtIndex:i+1] objectForKey:#"value"] floatValue];
check++;
if(check == 2)
{
break ;
}
}
}
if(i + 2 <= wallpaperPriceArray.count)
{
if(itemNumber >= [[wallpaperPriceArray objectAtIndex:i+2] intValue] && itemNumber < [[wallpaperPriceArray objectAtIndex:i+2] intValue])
{
wallpaperPriceValue = [[[wallpaperPriceArray objectAtIndex:i+2] objectForKey:#"value"] floatValue];
check++;
if(check == 2)
{
break ;
}
}
}

Answer 1

I Don't think the predicate is the right thing, Better would be to enumerate the objects here is some sample code:
NSArray *array = #[
#{ #"key" : #(1), #"value" : #(40)},
#{ #"key" : #(4), #"value" : #(50)},
#{ #"key" : #(8), #"value" : #(60)}
];
NSInteger searchedValue = 5; // <---
__block NSDictionary *closestDict = nil;
__block NSInteger closestValue = 0;
[array enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
NSDictionary *dict = obj;
NSInteger key = [dict[#"key"] integerValue];
// Check if we got better result
if(closestDict == nil || (key > closestValue && key <= searchedValue)){
closestDict = dict;
closestValue = key;
if(key == searchedValue) { *stop = YES; }
}
}];
NSLog(#"value %#", closestDict);

Answer 2

I would suggest in addition to above answer to use the spline method to get the value needed, this is in the link
https://github.com/soffes/SAMCubicSpline
Using this library would solve the question as follows:
NSArray *array = #[
#{ #"key" : #(1), #"value" : #(40)},
#{ #"key" : #(4), #"value" : #(50)},
#{ #"key" : #(8), #"value" : #(60)}];
SAMCubicSpline *spline = [[SAMCubicSpline alloc] initWithPoints:#[
[NSValue valueWithCGPoint:CGPointMake(1.0f, 40.0f)],
[NSValue valueWithCGPoint:CGPointMake(4.0f, 50f)],
[NSValue valueWithCGPoint:CGPointMake(8.0f, 60.0f)],
]];
then you can obtain any value by this
CGFloat y = [spline interpolate:x];