Two y axis in core plot graph with different axis scales

Question

I am programming a app where I have graph with two y axis and one x axis.left y axis has range from 0 to 20 so there are 20 majorTick axis.Right y axis has range from 0 to 10,so I want left y axis to be labelled for every alternate majorTickAxis.

here is my code snippet

//code
   CPTXYPlotSpace *plotSpace = (CPTXYPlotSpace *)self.graph.defaultPlotSpace;
float xmax=10.0;
float xmin=0.0;
plotSpace.xRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(xmin)      length:CPTDecimalFromFloat(xmax-xmin)];
float ymax=20.0;
float ymin=0.0;
float ymax2=10.0;
plotSpace.yRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(ymin) length:CPTDecimalFromFloat(ymax-ymin)];



// Grid line styles
CPTMutableLineStyle *majorGridLineStyle = [CPTMutableLineStyle lineStyle];
majorGridLineStyle.lineWidth = 0.75;
majorGridLineStyle.lineColor = [[CPTColor whiteColor] colorWithAlphaComponent:0.75];

CPTMutableLineStyle *minorGridLineStyle = [CPTMutableLineStyle lineStyle];
minorGridLineStyle.lineWidth = 0.25;
minorGridLineStyle.lineColor = [[CPTColor whiteColor] colorWithAlphaComponent:0.1];

CPTMutableLineStyle *redLineStyle = [CPTMutableLineStyle lineStyle];
redLineStyle.lineWidth = 2.0;
redLineStyle.lineColor = [[CPTColor redColor] colorWithAlphaComponent:0.5];                         

CPTMutableLineStyle *greenLineStyle = [CPTMutableLineStyle lineStyle];
greenLineStyle.lineWidth = 2.0;
greenLineStyle.lineColor = [[CPTColor greenColor] colorWithAlphaComponent:0.5];     

// Axes
CPTXYAxisSet *axisSet = (CPTXYAxisSet *)self.graph.axisSet;
CPTXYAxis *x          = axisSet.xAxis;
x.orthogonalCoordinateDecimal = CPTDecimalFromString(@"0");
x.majorIntervalLength = [[NSDecimalNumber decimalNumberWithString:@"1"] decimalValue];
x.minorTicksPerInterval       = 4;
x.labelOffset = 3.0f;
x.title         = @"Time";
x.titleOffset   = 20.0;
x.titleLocation = CPTDecimalFromFloat((xmax+xmin)/2);
x.majorGridLineStyle= majorGridLineStyle;
x.minorGridLineStyle=minorGridLineStyle;


CPTXYAxis *y = axisSet.yAxis;
y.majorIntervalLength         = CPTDecimalFromString(@"1.0");
y.majorTickLength=2.0f;
y.minorTicksPerInterval       = 4;
y.orthogonalCoordinateDecimal = CPTDecimalFromFloat(0.0);
y.labelExclusionRanges = [NSArray arrayWithObjects:
                          [CPTPlotRange plotRangeWithLocation:CPTDecimalFromInteger(0.0) 
                                                       length:CPTDecimalFromInteger(0.0)],Nil];
y.majorGridLineStyle= majorGridLineStyle;
y.minorGridLineStyle=minorGridLineStyle;


CPTXYAxis *y2 = [[(CPTXYAxis *)[CPTXYAxis alloc] initWithFrame:CGRectZero] autorelease];
y2.plotSpace    =plotSpace;     
y2.orthogonalCoordinateDecimal = CPTDecimalFromFloat(xmax);
y2.majorGridLineStyle=majorGridLineStyle;
y2.minorGridLineStyle=minorGridLineStyle;
y2.minorTicksPerInterval       = 4;
y2.majorIntervalLength        = CPTDecimalFromString(@"1.0");
y2.labelOffset        = 10.0;
y2.coordinate          =CPTCoordinateY;

y2.axisLineStyle       = x.axisLineStyle;
y2.labelTextStyle              = x.labelTextStyle;
y2.labelOffset                 = -30.0f;
y2.visibleRange                = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromInteger(0) length:CPTDecimalFromInteger(ymax2)];


y2.title                       = @"Temperature";
y2.titleLocation               = CPTDecimalFromInteger(5.0);
y2.titleTextStyle              =x.titleTextStyle;
y2.titleOffset                 =-45.0f;
y2.labelExclusionRanges = [NSArray arrayWithObjects:
                          [CPTPlotRange plotRangeWithLocation:CPTDecimalFromInteger(0.0) 
                                                       length:CPTDecimalFromInteger(0.0)],Nil];


self.graph.axisSet.axes = [NSArray arrayWithObjects:x, y, y2, nil];

// Create a plot that uses the data source method for red graph
CPTScatterPlot *redPlot = [[[CPTScatterPlot alloc] init] autorelease];
redPlot.identifier = @"red Plot";;

CPTMutableLineStyle *lineStyle = [[redPlot.dataLineStyle mutableCopy] autorelease];
lineStyle.miterLimit        = 1.0f;
redPlot.dataLineStyle = redLineStyle;
redPlot.dataSource = self;
redPlot.interpolation = CPTScatterPlotInterpolationStepped;

[self.graph addPlot:redPlot];

// Create a plot that uses the data source method for green graph
CPTScatterPlot *greenPlot = [[[CPTScatterPlot alloc] init] autorelease];
greenPlot.identifier = @"green Plot";;

CPTMutableLineStyle *greenlineStyle = [[greenPlot.dataLineStyle mutableCopy] autorelease];
greenlineStyle.miterLimit       = 1.0f;
greenPlot.dataLineStyle = greenLineStyle;
greenPlot.dataSource = self;
[self.graph addPlot:greenPlot];

 // Add some data
NSMutableArray *newData = [NSMutableArray arrayWithCapacity:100];
NSUInteger i;
for ( i = 0; i < 45; i++ ) {
    id x = [NSNumber numberWithDouble:i * 0.2];
    id y = [NSNumber numberWithDouble:i * rand() / ((double)RAND_MAX*5.0) ];        
    [newData addObject:[NSDictionary dictionaryWithObjectsAndKeys:
      x, @"x",y, @"y",nil]];
}
NSMutableArray *newData1 = [NSMutableArray arrayWithCapacity:100];
for ( i = 0; i < 45; i++ ) {
    id x =[NSNumber numberWithDouble:i * rand() / ((double)RAND_MAX*5.0) ]; 
    id y2 = [NSNumber numberWithDouble:i * 0.2];
    [newData1 addObject:[NSDictionary dictionaryWithObjectsAndKeys:
                        x, @"x",y2, @"y2",nil]];
}
self.plotData = newData;
self.plotData2=newData1;

Illdefined

Set the labelExclusionRanges to nil if you don't need it. – Pubis

Answer 1

If you want the two y-axes to have different scales, you need to add another plot space. Use the same xRange for the second plot space, but use a different yRange, e.g.,

CPTXYPlotSpace *plotSpace2 = [[[CPTXYPlotSpace alloc] init] autorelease];
plotSpace2.xRange = plotSpace.xRange;
plotSpace2.yRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(ymin)
                                                 length:CPTDecimalFromFloat(ymax2 - ymin)];
[graph addPlotSpace:plotSpace2];
y2.plotSpace = plotSpace2;

Use the majorIntervalLength to control the location of the ticks and grid lines:

y.majorIntervalLength = CPTDecimalFromFloat((ymax - ymin) / 10.0f);
y2.majorIntervalLength = CPTDecimalFromFloat((ymax2 - ymin) / 10.0f);

Pubis

hi Eric,Thanks a lot,your code was very helpful,Now i have different scales for both y axis – Illdefined

in case i use bars for displaying my values and i have two y axes with two plot spaces (where one is red and is green for example) and they use same x-axis, that will render them over each other so for example my red bar representing first value will be covered with green representing 2nd value at the same x-axis position. I would actually like those red and green bars to be kinda centered around x-axis value so they are both visible. Is that possible? – Furfuran

You can use the barOffset property to move the bars in one or both plots away from the normal center line so you can see both of them. – Pubis