Gradient Legend in Base

Gradient legend in base

Here is an example of how to build a legend from first principles using rasterImage from grDevices and layout to split the screen

layout(matrix(1:2,ncol=2), width = c(2,1),height = c(1,1))
plot(1:20, 1:20, pch = 19, cex=2, col = colfunc(20))

legend_image <- as.raster(matrix(colfunc(20), ncol=1))
plot(c(0,2),c(0,1),type = 'n', axes = F,xlab = '', ylab = '', main = 'legend title')
text(x=1.5, y = seq(0,1,l=5), labels = seq(0,1,l=5))
rasterImage(legend_image, 0, 0, 1,1)

Customize breaks on a color gradient legend using base R

The code in the original post is using the im class from the spatstat package. The plot command is dispatched to plot.im. Simply look at help(plot.im) to figure out how to control the colour ribbon. The relevant argument is ribargs. Here is a solution:

plot(Elevation_Map, col=custom(10), main="",
     ribargs=list(at=Elevation_Map$yrange, 
                  labels=c("Low Elevation", "High Elevation"),
                  las=1))

Adding a continuous color gradient legend strip to plot

The trick is to draw the color key as an image in a separate panel. Notice that I decrese the margin between the panels by reducing par(mar=...) and add an outer margin around both panels with par(oma=...).

my.palette <- rgb(ddf$VAL,256-ddf$VAL,0,maxColorValue=256)

# Create two panels side by side
layout(t(1:2), widths=c(5,1))

# Set margins and turn all axis labels horizontally (with `las=1`)
par(mar=rep(.5, 4), oma=rep(3, 4), las=1)

barplot(ddf$VAL,col=my.palette)

# Draw the color legend
image(1, ddf$VAL, t(seq_along(ddf$VAL)), col=my.palette, axes=FALSE)
axis(4)

2-D Scatter Plot with Gradient Color Legend on Top

Here's a ggplot alternative:

ggplot(data = mdf, aes(x = X, y = Y, col = Z)) +
  geom_point() +
  scale_colour_gradientn(colours = colourGradient) +
  theme_bw() +
  theme(legend.position = "top") +
  ggtitle("Y vs. X with Z-Color")

How to create vertical continuous legend without rotating the legend

<div id="container">
  <svg class="axis" style="background-color: rgba(255, 255, 255, 0.8); border-radius: 5px;">
    <defs>
        <linearGradient id="linear-gradient" x1="0%" x2="0%" y1="0%" y2="100%">
            <stop offset="0%" stop-color="#ff0000"></stop>
            <stop offset="25%" stop-color="#ffff00"></stop><stop offset="50%" stop-color="#00ff00"></stop>
            <stop offset="75%" stop-color="#00ffff"></stop><stop offset="100%" stop-color="#0000ff"></stop>
        </linearGradient></defs>
        <text class="legendTitle" x="25" y="10">Legend</text>
        <rect x="25" y="20" width="25" height="150" style="fill: url("#linear-gradient");"></rect>
          <g transform="translate(15, 55)" fill="none" font-size="10" font-family="sans-serif" text-anchor="middle" style="font-size: 10px; font-weight: 700;">
</svg>
</div>

How to plot different and independent color gradient legend in heatmap.2 (R)

I found this way:

# gplots contains the heatmap.2 function
library(gplots)

# create a matrix of random values from [0, 4]
random.matrix  <- matrix(runif(100, min = 0, max = 4), nrow = 10)

quantile.range <- quantile(random.matrix, probs = seq(0, 1))
palette.breaks <- seq(quantile.range["0%"], quantile.range["100%"], 0.25)

colfunc1 <- colorRampPalette(c("white", "red"))
colfunc2 <- colorRampPalette(c("white", "yellow"))
colfunc3 <- colorRampPalette(c("white", "green"))
colfunc4 <- colorRampPalette(c("grey", "black"))

color.palette  <- colorRampPalette(c(colfunc1(4), colfunc2(4), colfunc3(4), colfunc4(3)))(length(palette.breaks)-1)

heatmap.2(
  random.matrix,
  dendrogram = "none",
  scale      = "none",
  trace      = "none",
  symbreaks=FALSE,
  symkey=FALSE, 
  key        = TRUE,
  key.title = 'class information',
  key.xlab = 'class number',
  keysize = 2,
  #( "bottom.margin", "left.margin", "top.margin", "right.margin" )
  key.par=list(mar=c(3,3.5,2,0)),
  labRow     = NA,
  labCol     = NA,
  col    = color.palette,
  breaks = palette.breaks,
)
legend(x="topright", legend=c("class 1: city", "class 2: crops", "class 3: forest", "class 4: road"),fill=c("red", "yellow", "green", "grey", ""))

Reverse the direction of the color in linear gradient legend

You can change linerGradient to start from right. Right now you are filling from Left. You can do this by changing x1 and x2 in your gradient def.

linearGradient = defs
  .append("linearGradient")
  .attr("id", id)
  .attr("x1", "100%")  //Change this to 100%
  .attr("x2", horizontal ? "100%" : "0%") //This to 0%
  .attr("y1", "0%")
  .attr("y2", horizontal ? "0%" : "100%");

<div id="container">
  <svg class="axis" style="background-color: rgba(255, 255, 255, 0.8); border-radius: 5px;">
    <defs>
        <linearGradient id="linear-gradient" x1="100%" x2="0%" y1="0%" y2="0%">
            <stop offset="0%" stop-color="#ff0000"></stop>
            <stop offset="25%" stop-color="#ffff00"></stop><stop offset="50%" stop-color="#00ff00"></stop>
            <stop offset="75%" stop-color="#00ffff"></stop><stop offset="100%" stop-color="#0000ff"></stop>
        </linearGradient></defs>
        <text class="legendTitle" x="25" y="20">Legend</text>
        <rect x="25" y="30" width="250" height="25" style="fill: url("#linear-gradient");"></rect>
          <g transform="translate(15, 55)" fill="none" font-size="10" font-family="sans-serif" text-anchor="middle" style="font-size: 10px; font-weight: 700;">
          <path class="domain" stroke="currentColor" d="M10,6V0H258V6"></path>
          <g class="tick" opacity="1" transform="translate(10,0)">
            <line stroke="currentColor" y2="6"></line><text fill="currentColor" y="9" dy="0.71em">0.00</text><g>
          <g class="tick" opacity="1" transform="translate(258,0)"><line stroke="currentColor" y2="6"></line><text fill="currentColor" y="9" dy="0.71em">0.35</text></g></svg>
</div>

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