iPhone CorePlot proper formatting of y-axis

Question

I am using CorePlot to graph a set of data. Data for my x-axis consists of dates, while data for my y-axis consists of floats (which I then turn into NSNumber). I am getting data from a feed, and the feed returns numbers with a large number of decimals, eg: 0.46673718852844, 4.59392222219, 353.1293012045. I'm using the following piece of code to properly format y-axis:

NSNumberFormatter *numberFormatter = [[[NSNumberFormatter alloc] init] autorelease];
[numberFormatter setNumberStyle:NSNumberFormatterDecimalStyle];
[numberFormatter setMaximumFractionDigits:3];
[numberFormatter setPositiveFormat:@"###0.000"];    
CPTXYAxis *y = axisSet.yAxis;
y.labelingPolicy = CPTAxisLabelingPolicyAutomatic;
y.minorTicksPerInterval = 1;
y.preferredNumberOfMajorTicks = 5;
y.labelFormatter = numberFormatter;

In most cases, everything works fine. However, sometimes it displays the same value at multiple positions along the axis. See image below:

The values are presented correctly, I would just like to avoid unnecessary (0.466) labels. I've even tried to round the numbers to 3 decimals in numberForPlot method:

if(fieldEnum == CPTScatterPlotFieldY)
{ 
        float floatNum = r.value;
        floatNum *= 1000;
        int intValue = (int) floatNum;
        float decimal = floatNum - intValue;
        if (decimal > 0.5) {
            intValue++;
        }
        floatNum = intValue /1000.0;
        return [NSNumber numberWithFloat:floatNum];

}

but there is no difference in labels.

Answer 1

The preferredNumberOfMajorTicks property tells the labeling algorithm how many tick marks to use. If you want three ticks, set it to 3. You could also increase the maximum number of fraction digits for the number formatter to avoid the rounding issue altogether.