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scale scatter plot

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I'm drawing a scatter plot and in this case, all of my points (NSRect's) in pointsArray are float values between -1 and 1. My problem is that I can't seem to scale my view according to the values of my pointsArray. So, if my values are all between -1 and 1, my view size should show a scatter plot w/ x-axis boundaries -1 to 1, so as to show my points in proportion to the screen.

Can anyone help out w/ what I'm doing wrong here?

- (void) drawScatter
float xFactor = 0.0;
float yFactor = 0.0;

NSRect bounds = [self bounds];

float xabs = fabs(minXValue) + fabs(maxXValue);
float yabs = fabs(minYValue) + fabs(maxYValue);

xFactor = (bounds.size.width / 2) + (bounds.size.width * 0.10);
yFactor = (bounds.size.height / 2) + (bounds.size.height * 0.10);

// Move to origin in center of screen.
NSAffineTransform *xform = [NSAffineTransform transform];
[xform translateXBy:(bounds.size.width / 2) yBy:(bounds.size.height / 2)];

if (xFactor > yFactor) {
[xform scaleBy:(xFactor / 2)];
else {
[xform scaleBy:(yFactor / 2)];

id pp;

NSEnumerator *enumerator = [pointsArray objectEnumerator];

while (pp = [enumerator nextObject]) {
NSBezierPath *pointPath = [NSBezierPath bezierPath];
[pointPath appendBezierPathWithOvalInRect:[pp point]];
[pointPath transformUsingAffineTransform:xform];

if ([pp outputResult] > 0) {
[[NSColor redColor] setStroke];
[[NSColor whiteColor] setFill];
else {
[[NSColor blueColor] setStroke];
[[NSColor whiteColor] setFill];

[pointPath stroke];


- (void)drawRect:(NSRect) rect
NSRect bounds = [self bounds];

[[NSColor blackColor] setFill];
[NSBezierPath fillRect:bounds];

[self drawScatterPlotAxes];
[self drawScatter];

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