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In the Add Error Bars to Charts and Plots How To in the Mathematica documentation a function ErrorBar is given:

errorBar[type_: "Rectangle"][{{x0_, x1_}, {y0_, y1_}}, value_, meta_] := 
   Block[{error}, 
      error = Flatten[meta];
      error = If[error === {}, 0, Last[error]]; 
      {ChartElementData[type][{{x0, x1}, {y0, y1}}, value, meta], 
         {Black, Line[{
             {{(x0 + x1)/2, y1 - error}, {(x0 + x1)/2, y1 + error}}, 
             {{1/4 (3 x0 + x1), y1 + error}, {1/4 (x0 + 3 x1), y1 + error}}, 
             {{1/4 (3 x0 + x1), y1 - error}, {1/4 (x0 + 3 x1), y1 - error}}
            }]
       }}
      ]

that adds error bars to BarChart. Here is an example using some random data with random errors:

chartData = MapThread[{#1 -> #2} &, {RandomReal[1, 10], RandomReal[0.1, 10]}]

and some random labels:

labels = ToString /@ RandomReal[100000, 10]

Now plotting it, as per the tutorial:

BarChart[chartData, ChartElementFunction -> errorBar["Rectangle"], 
ChartLabels -> Placed[labels, Axis, Rotate[#, Pi/2] &]]

The labels are:

{"99539.6", "17862.9", "14683.4", "32667.2", "42690.", 
 "70230.8", "59050.4", "59204.7", "9138.2", "19080.3"}

However, in the plot:

Mathematica graphics

The first label is repeated incorrectly for all the bars, what's going on here? Without error bars the labels on the plot are correct:

Mathematica graphics

BarChart[RandomReal[1, 10], ChartLabels -> Placed[labels, Axis, Rotate[#, Pi/2] &]]
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In the original code, chartData is of the form {{value1 -> error1}, {value2 -> error2}, ... }, but it should be of the form {value1 -> error1, value2 -> error2, ... }. To get the right labels you could do something like (note the missing brackets in chartData)

chartData = 
 MapThread[#1 -> #2 &, {RandomReal[1, 10], RandomReal[0.1, 10]}];

BarChart[chartData, 
 ChartElementFunction -> errorBar["Rectangle"], 
 ChartLabels -> Placed[labels, Axis, Rotate[#, Pi/2] &]]

Mathematica graphics

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  • 2
    $\begingroup$ Why use #1 -> #2 & and not simply Rule? $\endgroup$ – Mr.Wizard Mar 7 '12 at 0:39
  • $\begingroup$ @Mr.Wizard I would suspect #1 -> #2& is less opaque than Rule as I don't know how many users know that they're equivalent. $\endgroup$ – rcollyer Mar 8 '12 at 18:20

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