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PubMatrixR

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Overview

PubMatrixR is an R package that performs systematic literature searches on PubMed and PMC databases using pairwise combinations of search terms. It creates co-occurrence matrices showing the number of publications that mention both terms from two different sets, enabling researchers to explore relationships between genes, diseases, pathways, or any other biomedical concepts.

This repository maintains and extends the original PubMatrixR package with improved validation, offline-safe tests/vignettes, and heatmap helpers.

Key Features

  • Pairwise Literature Search: Automatically searches all combinations of terms from two vectors
  • Multiple Database Support: Search PubMed or PMC databases via NCBI E-utilities
  • Static Visualizations: Generate heatmaps using pheatmap
  • Export Capabilities: Save results as CSV files with clickable hyperlinks to PubMed
  • Date Filtering: Restrict searches to specific publication date ranges
  • Flexible Input: Use vectors directly or read terms from a file
  • Progress Tracking: Built-in progress bars for long searches

Try it Online

Interactive Shiny App: https://toledoem.shinyapps.io/pubmatrix-app/

No installation required - just open the link and start analyzing!

Installation

CRAN 

install.packages("PubMatrixR")

GitHub (development version) 

# Install remotes if you haven't already
if (!requireNamespace("remotes", quietly = TRUE)) install.packages("remotes")

# Install PubMatrixR
remotes::install_github("ToledoEM/PubMatrixR-v2")

Dependencies

PubMatrixR requires the following R packages:

  • pbapply - Progress bars for apply functions
  • pheatmap - Static heatmap generation
  • xml2 - XML parsing for API responses
  • readODS - To export results in OpenDocument Spreadsheet - Excel compatible - for hyperlink export.

Quick Start 

library(PubMatrixR)

# Define two sets of search terms
genes_set1 <- c("SREBP1", "SOX4", "GLP1R")
genes_set2 <- c("NR1H4", "liver", "obesity")

# Perform the search and create a matrix
result <- PubMatrix(
  A = genes_set1,
  B = genes_set2,
  Database = "pubmed",
  daterange = c(2010, 2024),
  outfile = "my_results",
  export_format = "csv"  # Options: NULL (no export), "csv", or "ods"
)

# Create a heatmap with overlap percentages and Euclidean clustering
plot_pubmatrix_heatmap(result)

Function Documentation

PubMatrix()

The main function that performs pairwise literature searches and generates co-occurrence matrices.

Parameters

Parameter Type Default Description
file character - Path to file containing search terms (alternative to A/B vectors)
A character vector NULL First set of search terms
B character vector NULL Second set of search terms
API.key character NULL NCBI E-utilities API key (optional, increases rate limits)
Database character “pubmed” Database to search: “pubmed” or “pmc”
daterange numeric vector NULL Date range as c(start_year, end_year)
outfile character NULL Base filename for outputs (without extension). Required if export_format is specified.
export_format character NULL Export format for the hyperlinked results matrix. Options: NULL (default, no file export), ‘csv’ (Excel-compatible with HYPERLINK formulas), or ‘ods’ (LibreOffice/OpenOffice format).

Return Value

Returns a matrix-like data frame where:

  • Rows correspond to terms from vector B
  • Columns correspond to terms from vector A
  • Each cell contains the number of publications mentioning both terms

File Input Format

When using the file parameter, the input file should contain:

term1_from_A
term2_from_A
term3_from_A
#
term1_from_B
term2_from_B
term3_from_B

The # character separates the two sets of search terms.

Heatmap Functions

PubMatrixR provides dedicated functions for creating heatmaps from PubMatrix results.

plot_pubmatrix_heatmap()

Draws a heatmap, clustering rows and columns by Euclidean distance. Cells show the raw co-occurrence counts unless you pass values.

Cell value options
values Cell contents
"raw" (default) Publication co-occurrence counts
"row_pct" Each count as a percentage of its row total
"relative" count / (row_total + col_total - count) * 100

A warning about "relative": it is not a Jaccard index, and its numbers do not carry across runs. The totals in that formula are sums over whichever partner terms happen to be in your matrix, not the publication count for each term on its own. Add one unrelated term and every existing cell changes. Compare cells inside a single matrix with it if you like, but do not compare between matrices.

Heatmap Parameters
Parameter Type Default Description
matrix numeric matrix - A PubMatrix result matrix containing publication co-occurrence counts
title character “PubMatrix Co-occurrence Heatmap” Heatmap title
cluster_rows logical TRUE Whether to cluster rows using Euclidean distance
cluster_cols logical TRUE Whether to cluster columns using Euclidean distance
values character “raw” What each cell shows: “raw”, “row_pct”, or “relative”
show_numbers logical TRUE Display the plotted values in cells
filename character NULL Optional filename to save plot
Example 
# First generate a matrix
result <- PubMatrix(A = c("gene1", "gene2"), B = c("disease1", "disease2"))

# Create heatmap with overlap percentages and Euclidean clustering
plot_pubmatrix_heatmap(result)

# Save to file
plot_pubmatrix_heatmap(result, filename = "my_heatmap.png")

pubmatrix_heatmap()

Thin wrapper around plot_pubmatrix_heatmap() for quick visualization.

# Quick heatmap using defaults
pubmatrix_heatmap(result, title = "Quick PubMatrix Heatmap")

Examples

Basic Usage with Gene Symbols 

library(PubMatrixR)

# Define gene sets
genes_of_interest <- c("TP53", "BRCA1", "EGFR", "MYC")
pathways <- c("apoptosis", "DNA repair", "cell cycle", "oncogene")

# Perform search
results <- PubMatrix(
  A = genes_of_interest,
  B = pathways,
  Database = "pubmed",
  daterange = c(2015, 2024),
  outfile = "gene_pathway_matrix"
)

# View results
print(results)
#            TP53 BRCA1 EGFR  MYC
# apoptosis  1456   234  567  890
# DNA repair  789  1456  123  234
# cell cycle 1234   456  890  567
# oncogene    567   123  789 1456

Using MSigDB Gene Sets 

library(PubMatrixR)
library(msigdf)
library(dplyr)

# Extract gene symbols from MSigDB pathways
wnt_genes <- msigdf::msigdf.human %>%
  filter(grepl("wnt", geneset, ignore.case = TRUE)) %>%
  pull(symbol) %>%
  unique() %>%
  sample(10)  # Sample 10 genes for demonstration

obesity_genes <- msigdf::msigdf.human %>%
  filter(grepl("obesity", geneset, ignore.case = TRUE)) %>%
  pull(symbol) %>%
  unique() %>%
  sample(10)  # Sample 10 genes for demonstration

# Search for co-occurrences
wnt_obesity_matrix <- PubMatrix(
  A = wnt_genes,
  B = obesity_genes,
  Database = "pubmed",
  outfile = "wnt_obesity_cooccurrence"
)

# Create heatmap with overlap percentages and Euclidean clustering
plot_pubmatrix_heatmap(wnt_obesity_matrix)

Using File Input

Create a file called search_terms.txt:

insulin
glucose
diabetes
metabolic syndrome
#
liver
pancreas
adipose tissue
muscle

Then run:

results <- PubMatrix(
  file = "search_terms.txt",
  Database = "pubmed",
  daterange = c(2020, 2024),
  outfile = "metabolic_tissue_matrix"
)

# Create heatmap visualization
plot_pubmatrix_heatmap(results)

Advanced Example with API Key 

# Get better rate limits with an API key
results <- PubMatrix(
  A = c("CRISPR", "base editing", "prime editing"),
  B = c("therapeutic", "clinical trial", "safety"),
  API.key = "your_ncbi_api_key_here",
  Database = "pubmed",
  daterange = c(2020, 2024),
  outfile = "gene_editing_therapeutics"
)

Output Files

When outfile and export_format parameters are specified, PubMatrixR generates a results file with clickable hyperlinks:

Export Format Options

Format Parameter Value File Extension Use Case
No Export export_format = NULL (default) - Results returned only to R environment, no file saved
CSV export_format = "csv" .csv Excel-compatible format with HYPERLINK formulas for direct linking to PubMed searches
ODS export_format = "ods" .ods LibreOffice/OpenOffice format with embedded hyperlinks, better for cross-platform compatibility

Output File Format

The output filename follows the pattern: {outfile}_result.{extension}

All formats include:

  • Row names: Terms from vector B
  • Column names: Terms from vector A
  • Cell values: Publication co-occurrence counts with clickable hyperlinks to the corresponding PubMed search

Output Examples 

# No file export - results only in R
result <- PubMatrix(A = genes, B = diseases, Database = "pubmed")

# Export as CSV with hyperlinks
result <- PubMatrix(
  A = genes, 
  B = diseases, 
  Database = "pubmed",
  outfile = "my_results",
  export_format = "csv"
)
# Creates: my_results_result.csv

# Export as ODS (LibreOffice format)
result <- PubMatrix(
  A = genes, 
  B = diseases, 
  Database = "pubmed",
  outfile = "my_results",
  export_format = "ods"
)
# Creates: my_results_result.ods

Visualization

Create heatmaps using the dedicated heatmap functions:

# Basic heatmap: raw co-occurrence counts with Euclidean clustering
plot_pubmatrix_heatmap(your_matrix)

# Percentage views
plot_pubmatrix_heatmap(your_matrix, values = "row_pct")

# Save heatmap to file
plot_pubmatrix_heatmap(your_matrix,
                       filename = "my_heatmap.png",
                       title = "Custom Title")

Cells hold publication co-occurrence counts by default, or percentages if you set values. Rows and columns are clustered by Euclidean distance on whatever matrix ends up being plotted. The colour scale runs from light pink (#fee5d9) to dark red (#99000d), and saved output is 300 dpi, which is enough for print.

Performance Notes

  • Rate Limiting: NCBI allows 3 requests per second without an API key, 10 requests per second with a key
  • Search Time: Depends on matrix size (A × B combinations) and network speed
  • Progress Tracking: Built-in progress bars show search completion status
  • Memory Usage: Results are stored in memory; very large matrices may require substantial RAM

API Key Setup

To improve search speed and avoid rate limiting:

  1. Create a free NCBI account at https://account.ncbi.nlm.nih.gov/
  2. Go to Account Settings → API Key Management
  3. Generate a new API key
  4. Use the key in the API.key parameter

Reference: NCBI E-utilities documentation

Use Cases

PubMatrixR is particularly useful for:

  • Gene-Disease Association Studies: Explore literature connections between genes and diseases
  • Pathway Analysis: Investigate co-occurrence of genes within or across biological pathways
  • Drug-Target Research: Analyze relationships between compounds and potential targets
  • Systematic Literature Reviews: Quantify research coverage across multiple topics
  • Knowledge Gap Identification: Find under-researched combinations of terms
  • Bibliometric Analysis: Measure research activity in specific domains

Troubleshooting

Common Issues

Empty Results: If many searches return 0 results, try:

  • Using broader search terms
  • Expanding the date range
  • Checking spelling of scientific terms
  • Using alternative gene names or synonyms

Rate Limiting Errors: If you encounter HTTP 429 errors:

  • Obtain and use an NCBI API key
  • Reduce the size of your search matrix
  • Add delays between searches

Long Search Times: For large matrices:

  • Consider breaking into smaller sub-searches
  • Use more specific date ranges
  • Filter gene lists to most relevant terms

License

This project is licensed under the MIT License - see the LICENSE file for details.