This articles describes how to create and customize an **interactive heatmap in R** using the **heatmaply** R package, which is based on the *ggplot2* and *plotly.js* engine.

Contents:

## Prerequisites

Install the required R package:

`install.packages("heatmaply")`

Load the package:

`library("heatmaply")`

## Data preparation

Normalize the data to make the variables values comparable.

`df <- normalize(mtcars)`

Note that, other data transformation functions are `scale()`

(for standardization), `percentize()`

[for percentile transformation; available in the heatmaply R package]. Read more: How to Normalize and Standardize Data in R for Great Heatmap Visualization.

## Basic heatmap

`heatmaply(df)`

Heatmaply has also the option to produce a static heatmap using the `ggheatmap`

R function:

`ggheatmap(df)`

Note that, `heatmaply`

uses the seriation package to find an optimal ordering of rows and columns.

The function `heatmaply()`

has an option named `seriate`

, which possible values include:

`“OLO”`

(Optimal leaf ordering): This is the default value.`“mean”`

: This option gives the output we would get by default from heatmap functions in other packages such as`gplots::heatmap.2()`

.`“none”`

: This option gives us the dendrograms without any rotation. The result is similar to what we would get by default from hclust.

**Replicating the dendrogram ordering of gplots::heatmap.2()**.

- Create a heatmap using the
`gplots`

R package:

```
gplots::heatmap.2(
as.matrix(df),
trace = "none",
col = viridis(100),
key = FALSE
)
```

- Create a similar version using the
`heatmaply`

R package:

```
heatmaply(
as.matrix(df),
seriate = "mean",
row_dend_left = TRUE,
plot_method = "plotly"
)
```

## Split rows and columns dendrograms into k groups

The k-means algorithm is used.

```
heatmaply(
df,
k_col = 2,
k_row = 2
)
```

## Change color palettes

The default color palette is `viridis`

. Other excellent color palettes are available in the packages cetcolor and RColorBrewer.

Use the viridis colors with the option “magma”:

```
heatmaply(
df,
colors = viridis(n = 256, option = "magma"),
k_col = 2,
k_row = 2
)
```

Use the `RColorBrewer`

palette :

```
library(RColorBrewer)
heatmaply(
df,
colors = colorRampPalette(brewer.pal(3, "RdBu"))(256),
k_col = 2,
k_row = 2
)
```

Specify customized gradient colors using the function `scale_fill_gradient2()`

[ggplot2 package].

```
gradient_col <- ggplot2::scale_fill_gradient2(
low = "blue", high = "red",
midpoint = 0.5, limits = c(0, 1)
)
heatmaply(
df,
scale_fill_gradient_fun = gradient_col
)
```

## Customize dendrograms using dendextend

A user can supply their own dendrograms for the rows/columns of the heatmaply using the `Rowv`

and the `Colv`

parameters:

```
library(dendextend)
# Create dendrogram for rows
mycols <- c("#2E9FDF", "#00AFBB", "#E7B800", "#FC4E07")
row_dend <- df %>%
dist() %>%
hclust() %>%
as.dendrogram() %>%
set("branches_lwd", 1) %>%
set("branches_k_color", mycols[1:3], k = 3)
# Create dendrogram for columns
col_dend <- df %>%
t() %>%
dist() %>%
hclust() %>%
as.dendrogram() %>%
set("branches_lwd", 1) %>%
set("branches_k_color", mycols[1:2], k = 2)
```

```
# Visualize the heatmap
heatmaply(
df,
Rowv = row_dend,
Colv = col_dend
)
```

## Add annotation based on additional factors

The following R code adds annotation on column and row sides:

```
heatmaply(
df[, -c(8, 9)],
col_side_colors = c(rep(0, 5), rep(1, 4)),
row_side_colors = df[, 8:9]
)
```

## Add text annotations

By default, the colour of the text on each cell is chosen to ensure legibility, with black text shown over light cells and white text shown over dark cells.

`heatmaply(df, cellnote = mtcars)`

## Add custom hover text

```
mat <- df
mat[] <- paste("This cell is", rownames(mat))
mat[] <- lapply(colnames(mat), function(colname) {
paste0(mat[, colname], ", ", colname)
})
```

```
heatmaply(
df,
custom_hovertext = mat
)
```

## Saving your heatmaply into a file

Create an interactive html file:

```
dir.create("folder")
heatmaply(mtcars, file = "folder/heatmaply_plot.html")
browseURL("folder/heatmaply_plot.html")
```

Saving a static file (png/jpeg/pdf). Before the first time using this code you may need to first run: `webshot::install_phantomjs()`

or to install plotly’s orca program.

```
dir.create("folder")
heatmaply(mtcars, file = "folder/heatmaply_plot.png")
browseURL("folder/heatmaply_plot.png")
```

Save the file, without plotting it in the console:

```
tmp <- heatmaply(mtcars, file = "folder/heatmaply_plot.png")
rm(tmp)
```

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