How many bins in colorBin? about leaflet HOT 8 CLOSED

colorBin() is based on pretty(), and the price of making bins "pretty" is that it is you are unlikely to get exactly n bins. If you want to get exactly n bins, the cut points will not be "pretty" (e.g. numbers with 16 digits after the decimal point).

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@yihui great to know, but...

I think we should clearly spilt the problem in two:

• how many bins do I want to use? I must be able to specify the number of bins I want to use, either using colorBin (or colorFactor). If colorBin (or pretty()) decides for me how many bins is using, it is not (much) useful.
• what is the format of the data in the legend? On the legend data format issue I've already posted a feature request here. This discussion reinforces the need to address legend data formatting (maybe using the scale package?).

Suppose that I've used a not-pretty number of bins (e.g. with lots of decimals). I wouldn't see a problem if the legend data is just approximate: I would use a popup to display the actual value in each area to clarify any ambiguity. What would it matter to know precisely where the cut occurred? In most cases it wouldn't.

For me, a legend of a choropleth map needs to give an idea at a glance of the order of magnitude of the areas, especially if there is an easy way to get the actual detail (e.g. popup).

In any case, may I suggest to mention in the help that the number of bins are forced by pretty()?

At the moment it says only:

colorBin also maps continuous numeric data, but performs binning based on value (see the cut function).

Thanks

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@yihui As a way to extend the ability to define different binning approaches, I suggest to integrate the package ‘classInt’ by Roger Bivand.

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Thanks! I have addressed the documentation in #53, in which you will also be able to format the labels by yourself if you provide the bins vector of non-pretty numbers. Supporting classInt is trivial in the sense that you simply call classInt::classIntervals(var, n) and pass $brks to bins in colorBin(). I'd rather not introduce the dependency on another package.

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👍 thanks (but I would prefer pretty as an option...)

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@smartinsightsfromdata Just added an argument pretty = TRUE to colorBin(), so you can choose to use exactly n bins generated from seq(min, max, length = n).

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👍 👍

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I forgot to mention it was still in the PR #53 and has not been merged to the master branch yet.

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