title: core-plot, unable to plot two graphs
body: <p>I'm currently trying to use the core-plot library to graph some data I get via JSON. I'm trying to plot two graphs on the same chart but am unable to achieve this. When I simply plot just one chart, it works correctly.</p>
  
  <p>Below is my scatter plot code using the core-plot library.</p>
  
  <pre><code>#pragma mark -
  #pragma mark Plot construction methods
  
  - (void)constructScatterPlot
  {
      NSMutableArray *appleContentArray = [NSMutableArray arrayWithCapacity:270];
      NSMutableArray *googleContentArray = [NSMutableArray arrayWithCapacity:270];
  
      NSData *stocks = [NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://d1sz0kydzogekx.cloudfront.net/stocks.txt"]];
      NSInputStream *stockStream = [[NSInputStream alloc] initWithData:stocks];
      [stockStream open];
  
      NSUInteger i;
      i = 1;
  
      if (stockStream) {
          NSError *parseError = nil;
          id jsonObject = [NSJSONSerialization JSONObjectWithStream:stockStream options:NSJSONReadingAllowFragments error:&amp;parseError];
  
          if ([jsonObject respondsToSelector:@selector(objectForKey:)]) {
              for (NSDictionary *stock in [jsonObject objectForKey:@"stocks"]) {
                  if ([[stock objectForKey:@"stock"] isEqualToString:@"AAPL"]){
                      id x = [NSNumber numberWithInt:i];
                      id y = [stock objectForKey:@"close"];
  
                      [appleContentArray addObject:[NSMutableDictionary dictionaryWithObjectsAndKeys:x, @"x", y, @"y", nil]];
                  }
  
                  if ([[stock objectForKey:@"stock"] isEqualToString:@"GOOG"]){
                      id x = [NSNumber numberWithInt:i];
                      id y = [stock objectForKey:@"close"];
  
                      [googleContentArray addObject:[NSMutableDictionary dictionaryWithObjectsAndKeys:x, @"x", y, @"y", nil]];
                  }
  
                  i++;
              }
          }
  
      } else {
          NSLog(@"Failed to open stream.");
      }
  
      // Create graph from theme
      graph = [[CPTXYGraph alloc] initWithFrame:CGRectZero];
      CPTTheme *theme = [CPTTheme themeNamed:kCPTPlainBlackTheme];
      [graph applyTheme:theme];
      scatterPlotView.hostedGraph = graph;
  
      graph.paddingLeft = 0;
      graph.paddingTop = 0.0;
      graph.paddingRight = 0;
      graph.paddingBottom = 0;
  
      // Setup plot space
      CPTXYPlotSpace *plotSpace = (CPTXYPlotSpace *)graph.defaultPlotSpace;
      plotSpace.allowsUserInteraction = YES;
      plotSpace.xRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(-20.0) length:CPTDecimalFromFloat(260.0)];
      plotSpace.yRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(150.0) length:CPTDecimalFromFloat(400.0)];
  
      // Axes
      CPTXYAxisSet *axisSet = (CPTXYAxisSet *)graph.axisSet;
      CPTXYAxis *x = axisSet.xAxis;
      x.majorIntervalLength = CPTDecimalFromString(@"1000");
      x.orthogonalCoordinateDecimal = CPTDecimalFromString(@"2");
      x.minorTicksPerInterval = 2;
      NSArray *exclusionRanges = [NSArray arrayWithObjects:
                                  [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(1.99) length:CPTDecimalFromFloat(0.02)], 
                                  [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(0.99) length:CPTDecimalFromFloat(0.02)],
                                  [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(2.99) length:CPTDecimalFromFloat(0.02)],
                                  nil];
      x.labelExclusionRanges = exclusionRanges;
  
      CPTXYAxis *y = axisSet.yAxis;
      y.majorIntervalLength = CPTDecimalFromString(@"50");
      y.orthogonalCoordinateDecimal = CPTDecimalFromString(@"2");
      y.minorTicksPerInterval = 2;
  
      exclusionRanges = [NSArray arrayWithObjects:
                         [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(1.99) length:CPTDecimalFromFloat(0.02)], 
                         [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(0.99) length:CPTDecimalFromFloat(0.02)],
                         [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(3.99) length:CPTDecimalFromFloat(0.02)],
                         nil];
      y.labelExclusionRanges = exclusionRanges;
  
      // Create a green Apple plot area
      CPTScatterPlot *appleLinePlot = [[[CPTScatterPlot alloc] init] autorelease];
      appleLinePlot.identifier = @"Green Plot";
  
      CPTMutableLineStyle *appleLineStyle = [[appleLinePlot.dataLineStyle mutableCopy] autorelease];
  
      appleLineStyle.lineWidth = 2.0;
      appleLineStyle.lineColor = [CPTColor greenColor];
  
      appleLinePlot.dataLineStyle = appleLineStyle;
      appleLinePlot.opacity = 0.0f;
      appleLinePlot.cachePrecision = CPTPlotCachePrecisionDecimal;
  
      // Create a red Google plot area
      CPTScatterPlot *googleLinePlot = [[[CPTScatterPlot alloc] init] autorelease];
      googleLinePlot.identifier = @"Red Plot";
  
      CPTMutableLineStyle *googleLineStyle = [[googleLinePlot.dataLineStyle mutableCopy] autorelease];
  
      googleLineStyle.lineWidth = 2.0;
      googleLineStyle.lineColor = [CPTColor redColor];
      googleLinePlot.dataLineStyle = googleLineStyle;
  
      // Animate in the new plot
      CABasicAnimation *fadeInAnimation = [CABasicAnimation animationWithKeyPath:@"opacity"];
      fadeInAnimation.duration = 0.0f;
      fadeInAnimation.removedOnCompletion = NO;
      fadeInAnimation.fillMode = kCAFillModeForwards;
      fadeInAnimation.toValue = [NSNumber numberWithFloat:1.0];
      [appleLinePlot addAnimation:fadeInAnimation forKey:@"animateOpacity"];
      [googleLinePlot addAnimation:fadeInAnimation forKey:@"animateOpacity"];
  
      appleLinePlot.cachePrecision = CPTPlotCachePrecisionDecimal;
      googleLinePlot.cachePrecision = CPTPlotCachePrecisionDecimal;
  
      appleLinePlot.dataSource = self;
      self.dataForPlot = appleContentArray;
      [graph addPlot:appleLinePlot];
  
      googleLinePlot.dataSource = self;
      self.dataForPlot = googleContentArray;
      [graph addPlot:googleLinePlot];
  }
  
  #pragma mark -
  #pragma mark CPTBarPlot delegate method
  
  -(void)barPlot:(CPTBarPlot *)plot barWasSelectedAtRecordIndex:(NSUInteger)index
  {
      NSLog(@"barWasSelectedAtRecordIndex %d", index);
  }
  
  #pragma mark -
  #pragma mark Plot Data Source Methods
  
  -(NSUInteger)numberOfRecordsForPlot:(CPTPlot *)plot 
  {
      return [dataForPlot count];
  }
  
  -(NSNumber *)numberForPlot:(CPTPlot *)plot field:(NSUInteger)fieldEnum recordIndex:(NSUInteger)index 
  {
      NSDecimalNumber *num = nil;
  
      num = [[dataForPlot objectAtIndex:index] valueForKey:(fieldEnum == CPTScatterPlotFieldX ? @"x" : @"y")];
  
      if ( [(NSString *)plot.identifier isEqualToString:@"Green Plot"] ) {
          if ( fieldEnum == CPTScatterPlotFieldX ) {
              num = (NSDecimalNumber *)[NSDecimalNumber numberWithDouble:[num doubleValue]];
          }
  
          if ( fieldEnum == CPTScatterPlotFieldY ) {
              num = (NSDecimalNumber *)[NSDecimalNumber numberWithDouble:[num doubleValue]];
          }
      }
  
      if ( [(NSString *)plot.identifier isEqualToString:@"Red Plot"] ) {
          if ( fieldEnum == CPTScatterPlotFieldX ) {
              num = (NSDecimalNumber *)[NSDecimalNumber numberWithDouble:[num doubleValue]];
          }
      }
  
      return num;
  }
  </code></pre>