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I'm trying to get a BarChart to colour negative valued bars red and positive valued bars green but I'm having a time trying to do it. My latest attempt is:

data = {0.34`, 0.04`, 1.07`, -0.54`, -2.4`, 0.44`};
t = Piecewise[{{# >= 0, Green}}, Red] &;
BarChart[data, ChartLayout -> "Stepped", BarSpacing -> None,
 ColorFunction -> t, 
 ColorFunctionScaling -> False]

However this still colours the bars in the default colour. May someone tell me what I am doing wrong. I thought this would be pretty simple. I'm not getting an error. It just is ignoring the ColorFunction. I'm on 10.0.1

Thanks,

Edmund

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1 Answer 1

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You have inverted Piecewise arguments. Here is the right form:

data = {0.34, 0.04, 1.07, -0.54, -2.4, 0.44};
color=Piecewise[{{Green,# >= 0}}, Red] &;
BarChart[data
        ,ChartLayout -> "Stepped"
        ,BarSpacing -> None
        ,ColorFunction -> color
        ,ColorFunctionScaling -> False
    ]

Now it works:

enter image description here

I personaly prefer Which. Here is an example for accumulated color change using it:

color=Which[#<= 0,Red,True,Green]&;
BarChart[data
        ,ChartLayout -> "Stepped"
        ,BarSpacing -> None
        ,ChartStyle->color/@Accumulate@data
    ]

enter image description here

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  • $\begingroup$ Why is the last bar green ? $\endgroup$
    – eldo
    Oct 8, 2014 at 1:23
  • $\begingroup$ @Murta Thanks, that works great. But do you know why Piecewise isn't working? Shouldn't it work the same as Which? Also, I prefer Piecewise as it is not a programming construct as Which is. $\endgroup$
    – Edmund
    Oct 8, 2014 at 1:30
  • $\begingroup$ @Murta Why is the fourth bar red and the last one green ? $\endgroup$
    – eldo
    Oct 8, 2014 at 1:36
  • $\begingroup$ @eldo, it's a positive variation. So, it's green... $\endgroup$
    – Murta
    Oct 8, 2014 at 1:37
  • $\begingroup$ Why downvote? Someone knows? $\endgroup$
    – Murta
    Oct 8, 2014 at 1:42

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