---
title: "gVenn: Proportional Venn diagrams for genomic regions and gene set overlaps"
author: "Christophe Tav"
date: "August 2025"
output:
  html_document:
    toc: true
    toc_depth: 3
    number_sections: false
vignette: >
  %\VignetteIndexEntry{gVenn}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

```{r, echo=FALSE, out.width="20%", fig.align="center"}
knitr::include_graphics("figures/20250827_hex_gVenn_v1.png")
```

```{r, include = FALSE}
knitr::opts_chunk$set(
    collapse = TRUE,
    comment = "#>"
)
suppressWarnings(library(GenomicRanges))
```

# Introduction

**gVenn** stands for **gene/genomic Venn**.  
It provides tools to compute overlaps between genomic regions or sets of genes
and visualize them as **Venn** diagrams with areas proportional to the number of 
overlapping elements. In addition, the package can generate **UpSet** plots for
cases with many sets, offering a clear alternative to complex Venn diagrams.

With seamless support for `GRanges` and `GRangesList` objects, **gVenn**
integrates naturally into Bioconductor workflows such as ChIP-seq, ATAC-seq,
or other interval-based analyses.

Overlap groups can be easily extracted for further analysis, such as motif
enrichment, transcription factor binding enrichment, or gene annotation.
**gVenn** package produces clean, publication-ready figures.

<br>
```{r, echo=FALSE, out.width="100%", fig.align="center"}
knitr::include_graphics("figures/20250827_graphical_abstract_v2.png")
```
<br>

# Example workflow

This section demonstrates a typical workflow with gVenn, from computing overlaps to generating clean, publication-ready figures. The examples show how to work with genomic interval data.

We start by loading the package:
```{r setup}
library(gVenn)
```

## 1. Load example ChIP-seq genomic regions

We use the dataset **`a549_chipseq_dataset`**, which contains example consensus
peak subsets for **MED1**, **BRD4**, and **GR** after dexamethasone treatment
in A549 cells. To keep the dataset small and suitable for examples and tests,
each set has been restricted to peaks located on *chromosome 7*.  

These data originate from Tav *et al.* (2023)
<a href="https://doi.org/10.3389/fgene.2023.1237092" target="_blank">
doi:10.3389/fgene.2023.1237092</a>.

```{r, load_chip_dataset}
# Load the example A549 ChIP-seq peaks (subset on chr7 for demo)
data(a549_chipseq_peaks)
```
## 2. Compute overlaps between genomic regions

We compute overlaps between the ChIP-seq peak sets using `computeOverlaps()`:

```{r compute_overlaps}
genomic_overlaps <- computeOverlaps(a549_chipseq_peaks)
```

The result is a structured object that contains

- A GRanges object, where each region includes metadata describing its
overlap pattern across the input sets.
- An associated count matrix (or data frame) summarizing the number of
regions in each intersection.

## 3. Visualization

### Venn diagram
`plotVenn()` draws proportional Venn diagrams from the overlap object.

```{r, plot_venn, fig.width=5, fig.height=3, fig.align='center'}
plotVenn(genomic_overlaps)
```
<br>

### UpSet plot

For more than **three sets**, a Venn diagram with **areas exactly proportional**
to all intersections is **generally not mathematically attainable**. Solvers
(like those used by `eulerr`) provide **best-effort approximations**, but the
layout can become hard to read. In these cases, an **UpSet plot** is the
recommended visualization because it scales cleanly to many sets and preserves
intersection sizes precisely on bar axes.

We therefore suggest using `plotUpSet()` when you have **> 3 sets** (or any
time the Venn becomes visually crowded).

```{r, plot_upset, fig.width=5, fig.height=3, fig.align='center'}
plotUpSet(genomic_overlaps)
```
<br>

### Export visualization

You can export any visualization using `saveViz()`:

```{r save_plot, eval=FALSE}
venn <- plotVenn(genomic_overlaps)
saveViz(venn,
        output_dir = ".",
        output_file = "figure_gVenn",
        format = "pdf")
```

By default, files are written to the current directory (".").
If you enabled the date option (today), the current date will be prepended
to the filename.

You can also export to PNG or SVG:

```{r save_plot2, eval=FALSE}
saveViz(venn,
        output_dir = ".",
        output_file = "figure_gVenn",
        format = "png")

saveViz(venn,
        output_dir = ".",
        output_file = "figure_gVenn",
        format = "svg")
```

## 4. Extract elements per overlap group

```{r, extractOverlaps_example1}
groups <- extractOverlaps(genomic_overlaps)
```
```{r, extractOverlaps_example2}
# Display the number of genomic regions per overlap group
sapply(groups, length)
```
<br>

#### Overlap group naming
When overlaps are computed, each group of elements or genomic regions is
labeled with a binary code that indicates which sets the element belongs to.

- Each digit in the code corresponds to one input set (e.g., A, B, C).
- A 1 means the element is present in that set, while 0 means absent.
- The group names in the output are prefixed with "group_" for clarity.

<div align="center" width="50%">
| Group name   | Meaning                       |
|--------------|-------------------------------|
| `group_100`  | Elements only in **A**        |
| `group_010`  | Elements only in **B**        |
| `group_001`  | Elements only in **C**        |
| `group_110`  | Elements in **A ∩ B** (not C) |
| `group_101`  | Elements in **A ∩ C** (not B) |
| `group_011`  | Elements in **B ∩ C** (not A) |
| `group_111`  | Elements in **A ∩ B ∩ C**     |
</div>
<br>

#### Extract one particular group
Each overlap group can be accessed directly by name for downstream analyses,
including motif enrichment, transcription factor (TF) enrichment, annotation of
peaks to nearby genes, functional enrichment or visualization.

For example, to extract all elements that are present in **A ∩ B ∩ C**:

```{r, extractOverlaps_example3}
# Extract elements in group_111 (present in A, B, and C)
peaks_in_all_sets <- groups[["group_111"]]

# Display the elements
peaks_in_all_sets
```
<br>

#### Exporting overlap groups

Each overlap group (e.g., `group_100`, `group_110`, `group_111`) can be
exported for downstream analysis. The function `exportOverlaps()` writes
each group to a Excel file, which makes it easy to reuse the results outside of
R.

```{r, exportOverlaps, eval=FALSE}
# export overlpas
exportOverlaps(genomic_overlaps,
               output_dir = ".",
               output_file = "overlap_groups")
```

# Session info

```{r session-info}
sessionInfo()
```

# References

### Example A549 ChIP-seq dataset

- Tav, C., Fournier, É., Fournier, M., Khadangi, F., Baguette, A., Côté, M.C., Silveira, M.A.D., Bérubé-Simard, F.-A., Bourque, G., Droit, A., & Bilodeau, S. (2023).
*Glucocorticoid stimulation induces regionalized gene responses within topologically associating domains.*
**Frontiers in Genetics**, 14, 1237092.
<a href="https://doi.org/10.3389/fgene.2023.1237092" target="_blank">
doi:10.3389/fgene.2023.1237092
</a>

### Supporting packages

- **eulerr** :
Larsson, J. (2023).
*eulerr: Area-Proportional Euler and Venn Diagrams with Ellipses.*
<a href="https://CRAN.R-project.org/package=eulerr" target="_blank">
CRAN package page
</a>

- **ComplexHeatmap** :
Gu, Z., Eils, R., & Schlesner, M. (2016).
*Complex heatmaps reveal patterns and correlations in multidimensional genomic data.*
**Bioinformatics**, 32(18), 2847–2849.
<a href="https://doi.org/10.1093/bioinformatics/btw313" target="_blank">
doi:10.1093/bioinformatics/btw313
</a>
