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Topic: ListPlot - assigning a list of colors to a set of
Replies: 6   Last Post: Nov 6, 2013 12:29 AM

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Gordon Robertson

Posts: 18
Registered: 11/15/07
Re: ListPlot - assigning a list of colors to a set of
Posted: Nov 6, 2013 12:28 AM
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Thank you, Itai.

On 2013-11-04, at 9:08 PM, Itai Seggev wrote:

On Mon, Nov 04, 2013 at 11:16:19PM -0500, Gordon Robertson wrote:

I'm using Mathematica v9.x on a Mac, with OS X 10.7.5.

Could I ask about something that likely has a very simple solution? I have a list of XY coordinates for say 500 points that will become a scatterplot via ListPlot. I need to assign a colour to each point, using a list of labels (histology, risk, =85).

I've generated ArrayPlot graphics for cases like this for some time. For example, given some labels in column 4 of a 'hist' table:
colours = Table[{
Switch[name = hist[[i, 4]],
"Classical", Green, "Tall cell", Red, "Other", Blue]
}, {i, Length[hist]}];
ArrayPlot[{colours}, AspectRatio -> 0.1, Frame -> False]

For a ListPlot, I'd have thought that something as simple as dropping a list of colours into a PlotStyle Directive would do the job. But the following line plots three blue points, rather than a Red, Green and Blue point.
ListPlot[{{1, 1}, {2, 2}, {3, 3}},
PlotStyle -> Directive[PointSize[0.02], {Red, Green, Blue}]]

You have two issues. The first is that you misunderstand Directive. A
Directive represent a single style, both semantically and practically. It can
never represent a group styles.

The second is that ListPlot assigns colors on a per dataset basis, not per
point. So assuming you wish to repeat cyclically and each point needs its own
color, you can do something like

ListPlot[List /@ {{1, 1}, {2, 2}, {3, 3}},
PlotStyle -> {Directive[PointSize[0.02`], RGBColor[1, 0, 0]],
Directive[PointSize[0.02`], RGBColor[0, 1, 0]],
Directive[PointSize[0.02`], RGBColor[0, 0, 1]]}]

Is there a simple way to declare a list of colours in ListPlot? I've looked through the PlotStyle documentation, and apologize if I've missed seeing how to do this.

Thanks very much for your help.

Gordon Robertson
Michael Smith Genome Sciences Centre
BC Cancer Agency
Vancouver BC Canada
Itai Seggev
Mathematica Algorithms R&D

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