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I have the following data set that I need to display on the heat map:

[ 30, 15, 66, 7, 9999, 78, 42, 132 ]

So if I map the values to the color scale using a linear function I only see the spike while the rest of the values I cannot tell apart because the difference between them is insignificant in the scale of that spike.

I tried a log function but it didn't get a good looking picture either.

I don't care about accurate correspondence between the value and the color intensity.

Is there a way to map the values to the color scale so that the difference between all values was visible? Can I mitigate that spike somehow? I am asking about established approaches or algorithms addressing problems like this.

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  • $\begingroup$ Consider mapping the data that is within N standard deviations of the mean to the heat map with special colors/symbols for the outliers. $\endgroup$
    – MichaelT
    Mar 27, 2013 at 14:45
  • $\begingroup$ You could try to renumber them by their position if you would sort them ([3,2,4,1,8,6,5,7]). If you get more distinct numbers than colors, you can combine multiple as one (either those whose value is close or log(value) is close (or some other function). $\endgroup$
    – user470365
    Mar 27, 2013 at 15:10
  • $\begingroup$ Very closely related: stats.stackexchange.com/questions/51792/…. Does this answer your question? $\endgroup$
    – whuber ♦
    Mar 27, 2013 at 19:44
  • $\begingroup$ I would have set a treshshold, computing another vector v such that vi= min(200, xi). $\endgroup$
    – lcrmorin
    Mar 27, 2013 at 19:53

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There are many different ways of handling outliers, as well as answers to similar questions here already. I would recommend taking a look at

The first deals with this problem in R. Taking the approach of graphing the non-outliers with a heatmap, then overlaying the outliers and annotating the legend to describe that this is what was done.

The second contains links to general solutions and approaches to outliers.

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