Understanding and Solving PDF Download Name Issues

As a data scientist or researcher, downloading files from databases is an essential task. However, dealing with named files can be challenging, especially when working with PDFs. In this article, we’ll explore the issues surrounding PDF file naming after download, discuss potential causes and solutions, and provide code examples to help you overcome these challenges.

Introduction

The problem at hand is that when downloading multiple PDF files using R or any other programming language, the file names do not match the expected naming convention. In this case, we’re dealing with a specific scenario involving UN organization databases, but the issue is generally applicable to any data download process.

Understanding Regular Expressions

To address this problem, we need to understand regular expressions (regex). Regex is a powerful tool for matching patterns in strings. It’s used extensively in text processing and string manipulation tasks.

In our case, we’re interested in extracting the Unique ID from URLs that contain it. The str_match function from the R stringr package tries to match the URL against a given pattern. However, when using str_match, it returns the matched part of the string, which is not always what we want.

The Issue with str_match

Let’s dive into the issue at hand. The problem arises because str_match doesn’t return the entire matched string if the pattern is not found. Instead, it returns a vector containing non-matching parts and NA values for missing matches.

Here’s an example:

# Test URL with Unique ID
myurl <- "http://www.ilo.org/evalinfo/product/download.do?type=document&id=8287"

# str_match using the URL as input
matches <- str_match(myurl, "UniqueID=(.+)")

When you run this code, matches will contain a single element with value "NA", indicating that no match was found.

Solving PDF Download Name Issues

To overcome this issue, we need to use regular expressions to extract the Unique ID from the URL. We can achieve this using the str_extract function from the R stringr package.

Here’s an example:

# Test URL with Unique ID
myurl <- "http://www.ilo.org/evalinfo/product/download.do?type=document&id=8287"

# Extract Unique ID using str_extract
id_value <- str_extract(myurl, "(?<=id=)\\d+")

In this example, we use the (?<=...) syntax to match any number of digits (\d+) that follow immediately after id=. This ensures that we extract the correct Unique ID value from the URL.

Code Example: Downloading and Naming PDF Files

Let’s put it all together with a code example:

# Load necessary libraries
library(downloader)
library(stringr)

# Vector of test URLs
pdfscollect <- c(
  "<a>http://www.ilo.org/evalinfo/product/download.do?type=document&id=8287</a>",
  "<a>http://www.ilo.org/evalinfo/product/download.do?type=document&id=10523</a>",
  # ... add more URLs as needed
)

# Function to download and name PDF files
download_and_name_pdf <- function(url) {
  # Extract Unique ID using str_extract
  id_value <- str_extract(url, "(?<=id=)\\d+")

  # Create file name
  filename <- paste("collected/", id_value, ".pdf", sep = "")

  # Download and save PDF file
  download(url, filename)

  # Return the downloaded file path
  return(filename)
}

# Loop through URLs and download PDF files
for (url in pdfscollect) {
  filename <- download_and_name_pdf(url)
  cat("Downloaded file:", filename, "\n")
}

In this example, we define a function download_and_name_pdf that takes a URL as input. It extracts the Unique ID using str_extract, creates a file name by concatenating the extracted ID with an “.pdf” extension, and downloads the PDF file using R’s built-in download function.

We then loop through the vector of test URLs and call the download_and_name_pdf function for each URL. The downloaded file paths are printed to the console for verification.

Conclusion

In this article, we discussed the issues surrounding PDF download naming and provided a solution using regular expressions. By understanding how str_match works and using alternative approaches like str_extract, we can extract the expected data from URLs and create meaningful file names.

The code example demonstrates how to implement this approach in R, and you can adapt it to your specific programming language of choice. Remember to always verify the output by printing the downloaded file paths or checking their contents for accuracy.

I hope this article has helped you overcome challenges with PDF download naming!

Last modified on 2024-04-02