Plot data & show outlier with differ...

[Tariq]

Hello,

I have plotted some data in a graph as point graph, with this following code:

$graphdata = array();
while($row = mysql_fetch_array($result))
{
$graphdata [] = array('',$row['Height'],$row['Speed']);
}
$plot = new PHPlot(800, 600);
$plot->SetImageBorderType('plain');
$plot->SetDataType('data-data');

$plot->SetPlotType('points');
$plot->SetDataValues($graphdata);

$plot->SetTitle('Height vs Speed');

$plot->SetXTickIncrement(1.0);
$plot->SetXTickAnchor(0.5);

$plot->SetPlotAreaPixels(NULL, 40, 780, NULL);
$plot->SetCallback('draw_graph', NULL, NULL);

$plot->DrawGraph();

The plot is drawn nicely. Now, I want to show the outliers within this data
points and show them in different color point. I have already detected which
points are the outliers.

Suppose, my data array from the above MySQL query is:

Height Speed

---

23 12

24 23

41 33

18 22

17 21

5 21

21 33

I have taken Height in X-axis and Speed in Y axis and plotted them. Now, I got
the Outliers by running another MySQL query and the Outliers are:

Height Speed

---

41 33

5 21

Now, how can I color differently (say, in red color) these 2 outliers on the
graph which I have drawn before?

Please let me know if you need more information about my problem statement.

Any help will be appreciated.

[lbayuk]

I can think of 4 ways to do this: multiple data sets, a custom data color
callback function, multiple plot overlay, or a plot annotation callback. The
first 2 are probably best here, so that's what I will describe.

1. Use multiple data sets (more than one Y value for each X, but only one of them will have an actual value). Each data set uses a different color, so by moving your outliers to a second data set, then will be plotted in the second color. For a normal point, a row in your data array would look like this: array('', $row, $row, ''). For an outlier, it would look like this: array('', $row, '', $row). You can extend this to more colors (but it gets a little awkward building the data array). Note PHPlot ignores the points with Y = ''.

2. Use a Custom Data Color callback function. This is a PHP function you write that PHPlot will call when it needs a color for a data point. Your function then has complete control over the colors. You can use the standard color for your normal points, and a different color for your outliers.

The PHPlot manual has a reference
section and example on using this feature.

[Tariq]

Okay, thanks. I will try them. If I face some difficulties, I will post it
here.

[Tariq]

I used the first approach and it worked perfectly. So many thanks for the
tips.

One more quick question: now the normal data points are plotted in blue color
and the outliers are in green colors. Using this approach, is there any way to
specify the color for outliers?

[lbayuk]

Of course. For example, $plot->SetDataColors(array('red', 'blue')) makes the
first Y value set red, and the second blue.

[Tariq]

Great! Thanks.