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POSetting breakpoints for data with scale_fill_brewer() function in ggplot2
 

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  1. POSetting breakpoints for data with scale_fill_brewer() function in ggplot2
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    <p>I am creating a map (choropleth) as described on the <a href="https://github.com/hadley/ggplot2/wiki/plotting-polygon-shapefiles" rel="nofollow noreferrer">ggplot2 wiki</a>. Everything works like a charm, except that I am running into an issue mapping a continuous value to the polygon fill color via the scale_fill_brewer() function.</p> <p><a href="https://stackoverflow.com/questions/5996513/change-colour-scheme-for-ggplot-geom-polygon-in-r">This question</a> describes the problem I'm having. As in the answer, my workaround has been to pre-cut my data into bins using the gtools quantcut() function:</p> <p><strong>UPDATE: This first example is actually the right way to do this</strong></p> <pre><code>require(gtools) # needed for quantcut() ... fill_factor &lt;- quantcut(fill_continuous, q=seq(0,1,by=0.25)) ggplot(mydata) + aes(long,lat,group=group,fill=fill_factor) + geom_polygon() + scale_fill_brewer(name="mybins", palette="PuOr") </code></pre> <p>This works, however, I feel like I should be able to skip the step of pre-cutting my data and do something like this with the breaks option:</p> <pre><code>ggplot(mydata) + aes(long,lat,group=group,fill=fill_continuous) + geom_polygon() + scale_fill_brewer(names="mybins", palette="PuOr", breaks=quantile(fill_continuous)) </code></pre> <p>But this doesn't work. Instead I get an error something like:</p> <blockquote> <p>Continuous variable (composite score) supplied to discrete scale_brewer.</p> </blockquote> <p>Have I misunderstood the purpose of the "breaks" option? Or is breaks broken?</p>
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      1. POSetting breakpoints for data with scale_fill_brewer() function in ggplot2
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    1. COAs the error says `scale_fill_brewer` is for discrete data, not continuous.
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    2. COThanks, Hadley--for the answer and for writing the package. I think I was assuming that continuous data + breaks = discrete. Does that mean that my first example (pre-cutting my continuous data) is the 'right' way to do this?
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    3. COYes. Legends are no different to axes - setting breaks on an axis doesn't make the data discrete, it just moves the tick marks around.
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