Core-Plot how to pack data

Question

I was wondering how I need to prepare the data so it is ready for core-plot.

one line per year
dayOfYear in the x-axis
value on the y-axis

My x-axis has 366 points (Each day of the year). At the moment I have a dictionary that looks like this

 2009 (year) =     {
        151 (dayofyear) = 5 (value);
        192 = 25;
        206 = 5;
        234 = 20;
        235 = 20;
        255 = 20;
        262 = 10;
        276 = 10;
        290 = 10;
        298 = 7;
        310 = 1;
        338 = 3;
        354 = 5;
        362 = 5;
    };
    2010 =     {
        114 = 7;
        119 = 3;
        144 = 7;
        17 = 5;
        187 = 10;
        198 = 7;
        205 = 10;
        212 = 10;
        213 = 20;
        215 = 5;
        247 = 10;
        248 = 10;
        256 = 10;
        262 = 7;
        264 = 10;
        277 = 10;
        282 = 3;
        284 = 7;
        47 = 5;
        75 = 7;
        99 = 7;
    };
    2011 =     {
        260 = 10;
    };

I think core-plot needs an array doesn't it? How would you pack this to be the most efficient?

Eric Skroch Eric Skroch · Accepted Answer · 2011-09-22T00:50:16

The choice of data structure is completely up to you. You already have the data in a dictionary, so keep that. Implement the following method in your datasource:

-(NSNumber *)numberForPlot:(CPTPlot *)plot
                     field:(NSUInteger)fieldEnum
               recordIndex:(NSUInteger)index;

Assuming you have a separate plot for each year, use the plot parameter to select the appropriate year dictionary from the data dictionary. Use the fieldEnum parameter to determine whether the plot is asking for the x or y value and the index parameter to decide which value in the list to return.

For instance (assuming all values in the dictionaries are stored as NSNumber objects and you're using a scatter plot):

-(NSNumber *)numberForPlot:(CPTPlot *)plot
                     field:(NSUInteger)fieldEnum
               recordIndex:(NSUInteger)index
{
    NSDictionary *year = // retrieve the year dictionary based on the plot parameter

    NSDictionary *yearData = [year objectAtIndex:index];

    NSNumber *num = nil;

    switch ( fieldEnum ) {
        case CPTScatterPlotFieldX:
            num = [yearData objectForKey:@"dayofyear"];
            break;

        case CPTScatterPlotFieldY:
            num = [yearData objectForKey:@"value"];
            break;

        default:
            break;
    }

    return num;
}

Core-Plot how to pack data

2 Answers