Removing Texts from a Corpus in R

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In this article, we will explore how to remove unwanted texts from a corpus in R using the quanteda package.

Introduction

The corpus_segment() function in the tm package is used to segment a text into smaller parts based on a given pattern. However, sometimes you might want to remove certain segments from the corpus. In this article, we will show how to use the quanteda package to achieve this.

Prerequisites

Before proceeding with this article, make sure you have installed and loaded the necessary packages in R:

# Install required packages
install.packages("quanteda")
install.packages("tm")
install.packages("readtext")

# Load required packages
library(quanteda)
library(tm)
library(readtext)

Creating a Corpus

First, we need to create a corpus from a text file. In this example, we will use the readtext package to read a text file and then convert it into a corpus.

# Create a corpus from a text file
frp2005 <- readtext::readtext("http://www.nsd.uib.no/polsys/data/filer/parti/H9368.html", encoding = "LATIN1")

Segmenting the Text

Next, we use the corpus_segment() function to segment the text into smaller parts based on a given pattern. In this example, we are using a regular expression to segment the text.

# Segment the text into smaller parts
tmp <- corpus(frp2005)
docvars(tmp, c("parti", "2005")) <- c("frp", 1)

frp_2005 <- tmp %>%
  corpus_segment(
    pattern = "\n[A-Z][a-z].*\\w\n.\\w",
    valuetype = "regex",
    case_insensitive = FALSE
  )

Removing Unwanted Segments

Now that we have segmented the text, we can use the corpus_subset() function to remove unwanted segments from the corpus.

# Remove unwanted segments from the corpus
frp_2005_subset <- corpus_subset(frp_2005, !docnames(frp_2005) %in% c("H9368.html.4"))

Example Use Cases

Here are some example use cases for removing unwanted segments from a corpus:

Removing documents with certain keywords: You can remove documents that contain certain keywords by using the grepl() function.

Remove documents that contain the keyword “H9368.html.4”

frp_2005_subset <- corpus_subset(frp_2005, !grepl(“H9368\.html\.[45]”, docnames(frp_2005)))


*   Removing documents with certain lengths: You can remove documents of a certain length by using the `str_length()` function.
    ```markdown
# Remove documents that are less than 100 words
frp_2005_subset <- corpus_subset(frp_2005, !str_length(docnames(frp_2005)) < 100)

Conclusion

In this article, we have shown how to remove unwanted texts from a corpus in R using the quanteda package. We covered the basics of creating a corpus, segmenting text, and removing unwanted segments. We also provided some example use cases for removing documents based on certain criteria.

By following these steps, you can easily remove unwanted segments from your corpus and improve the quality of your analysis.

Additional Tips

Make sure to adjust the regular expression pattern according to your needs.
Use the grepl() function to search for patterns in document names or token sequences.
Use the str_length() function to check the length of documents.

Last modified on 2024-05-02