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# geom_raster in ggplot2

How to make a 2-dimensional heatmap in ggplot2 using geom_raster.

New to Plotly?

Plotly is a free and open-source graphing library for R. We recommend you read our Getting Started guide for the latest installation or upgrade instructions, then move on to our Plotly Fundamentals tutorials or dive straight in to some Basic Charts tutorials.

### Basic 2d Heatmap

geom_raster creates a coloured heatmap, with two variables acting as the x- and y-coordinates and a third variable mapping onto a colour. (It is coded similarly to geom_tile and is generated more quickly.) This uses the volcano dataset that comes pre-loaded with R.

library(reshape2)
library(plotly)

df <- melt(volcano)

p <- ggplot(df, aes(Var1, Var2)) +
geom_raster(aes(fill=value)) +
labs(x="West to East",
y="North to South",
title = "Elevation map of Maunga Whau")

ggplotly(p)


### Customized 2d Heatmap

This uses the Spectral palette from ColorBrewer; a full list of palettes is here.

library(reshape2)
library(plotly)

df <- melt(volcano)

p <- ggplot(df, aes(Var1, Var2)) +
geom_raster(aes(fill=value)) +
scale_fill_distiller(palette = "Spectral", direction = -1) +
labs(x="West to East",
y="North to South",
title = "Elevation map of Maunga Whau",
fill = "Elevation") +
theme(text = element_text(family = 'Fira Sans'),
plot.title = element_text(hjust = 0.5))

ggplotly(p)


### What About Dash?

Dash for R is an open-source framework for building analytical applications, with no Javascript required, and it is tightly integrated with the Plotly graphing library.

Learn about how to install Dash for R at https://dashr.plot.ly/installation.

Everywhere in this page that you see fig, you can display the same figure in a Dash for R application by passing it to the figure argument of the Graph component from the built-in dashCoreComponents package like this:

library(plotly)

fig <- plot_ly()
# fig <- fig %>% add_trace( ... )
# fig <- fig %>% layout( ... )

library(dash)
library(dashCoreComponents)
library(dashHtmlComponents)

app <- Dash$new() app$layout(
htmlDiv(
list(
dccGraph(figure=fig)
)
)
)

app\$run_server(debug=TRUE, dev_tools_hot_reload=FALSE) 