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POHow to legend a raster using directly the raster attribute table and displaying the legend only for class displayed in the raster?
 

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  1. POHow to legend a raster using directly the raster attribute table and displaying the legend only for class displayed in the raster?
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    <p>I would like to use the raster attribute table information to create the legend of a raster such as the raster <a href="https://i.stack.imgur.com/tgC2P.png" rel="nofollow noreferrer">1</a> and display the legend only for the class displayed in the raster. I build an example to explain what I would like to get.</p> <p><strong>1/ Build the raster</strong></p> <pre><code>r &lt;- raster(ncol=10, nrow=10) values(r) &lt;-sample(1:3,ncell(r),replace=T) </code></pre> <p><strong>2/ Add the Raster Attribute Table</strong></p> <pre><code>r &lt;- ratify(r) # build the Raster Attibute table rat &lt;- levels(r)[[1]]#get the values of the unique cell frot the attribute table rat$legend &lt;- c('Class A', 'Class B', 'Class C') levels(r) &lt;- rat </code></pre> <p><strong>3/ Plot the raster</strong> Fig <a href="https://i.stack.imgur.com/tgC2P.png" rel="nofollow noreferrer">1</a></p> <pre><code>my_col=c('blue','red','green') plot(r,col=my_col,legend=F,box=F,axes=F) legend(x='top', legend =rat$legend,fill = my_col) </code></pre> <p>I would like to replace the <code>legend =rat$legend</code> parammeter by a properties of the raster linked to the ratser attribute table. I have tried different combination using <code>levels()</code> such as <code>c(levels(r)[[1]][1])</code> but I generate a list and not a character not usable in the legend parameter.</p> <p><strong>4/ Crop and plot the raster to a part with only 2 classes (here the 4 pixels at the down right extent)</strong> Fig <a href="https://i.stack.imgur.com/VzF8M.png" rel="nofollow noreferrer">2</a></p> <pre><code>rcrop&lt;-crop(r,extent(r,9,10,9,10)) plot(rcrop,col=my_col,legend=F,box=F,axes=F) </code></pre> <p>For this second fig, I thus would like to diplay automatically only the legend of the class displayed on the raster <a href="https://i.stack.imgur.com/VzF8M.png" rel="nofollow noreferrer">2</a>.</p> <p><img src="https://i.stack.imgur.com/VzF8M.png" alt="Raster with legend"></p> <p><img src="https://i.stack.imgur.com/tgC2P.png" alt="Cropped raster with legend"></p> <hr> <p>Here is the solution proposed by Roman <a href="https://i.stack.imgur.com/hAJdN.png" rel="nofollow noreferrer">4</a>. <img src="https://i.stack.imgur.com/hAJdN.png" alt="Solution proposed by Roman"></p>
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      1. POHow to legend a raster using directly the raster attribute table and displaying the legend only for class displayed in the raster?
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      1. POHow to legend a raster using directly the raster attribute table and displaying the legend only for class displayed in the raster?
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      1. POHow to legend a raster using directly the raster attribute table and displaying the legend only for class displayed in the raster?
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    1. CORoman's answer is good; just wanted to point out that if you have a `list` and want a character vector, you can always do `as.character(unlist(mylist))`
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      1. POHow to legend a raster using directly the raster attribute table and displaying the legend only for class displayed in the raster?
      1. USCarl Witthoft
    2. CO@Carl : Thanks, indeed when I use 'legend(x='top', legend =as.character(unlist( c(levels(r)[[1]][2]))),fill = my_col)' , I directly get the legend from the attribute raster table. Anyway, the Roman's answer does not solve the problem as it create a new legend not based on the raster attribute table. I'm thus losing the 'Class A',... legend
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      1. POHow to legend a raster using directly the raster attribute table and displaying the legend only for class displayed in the raster?
      1. USWraf
 

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