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# lexRankr: Extractive Text Summariztion in R
[](https://travis-ci.org/AdamSpannbauer/lexRankr) [](https://ci.appveyor.com/project/AdamSpannbauer/lexRankr) [](https://codecov.io/github/AdamSpannbauer/lexRankr?branch=master) [](https://CRAN.R-project.org/package=lexRankr)  [](https://github.com/AdamSpannbauer/lexRankr/commits/master)
## Installation
```r
##install from CRAN
install.packages("lexRankr")
#install from this github repo
devtools::install_github("AdamSpannbauer/lexRankr")
```
## Overview
lexRankr is an R implementation of the LexRank algorithm discussed by Güneş Erkan & Dragomir R. Radev in [LexRank: Graph-based Lexical Centrality as Salience in Text Summarization](http://www.cs.cmu.edu/afs/cs/project/jair/pub/volume22/erkan04a-html/erkan04a.html). LexRank is designed to summarize a cluster of documents by proposing which sentences subsume the most information in that particular set of documents. The algorithm may not perform well on a set of unclustered/unrelated set of documents. As the white paper's title suggests, the sentences are ranked based on their centrality in a graph. The graph is built upon the pairwise similarities of the sentences (where similarity is measured with a modified idf cosine similarity function). The paper describes multiple ways to calculate centrality and these options are available in the R package. The sentences can be ranked according to their degree of centrality or by using the Page Rank algorithm (both of these methods require setting a minimum similarity threshold for a sentence pair to be included in the graph). A third variation is Continuous LexRank which does not require a minimum similarity threshold, but rather uses a weighted graph of sentences as the input to Page Rank.
*note: the lexrank algorithm is designed to work on a cluster of documents. LexRank is built on the idea that a cluster of docs will focus on similar topics*
*note: pairwise sentence similarity is calculated for the entire set of documents passed to the function. This can be a computationally instensive process (esp with a large set of documents)*
## Basic Usage
```r
library(lexRankr)
library(dplyr)
df <- tibble(doc_id = 1:3,
text = c("Testing the system. Second sentence for you.",
"System testing the tidy documents df.",
"Documents will be parsed and lexranked."))
df %>%
unnest_sentences(sents, text) %>%
bind_lexrank(sents, doc_id, level = 'sentences') %>%
arrange(desc(lexrank))
```
## More Examples
* [Vignette](https://CRAN.R-project.org/package=lexRankr/vignettes/Analyzing_Twitter_with_LexRankr.html)
* [Summarizing Web Articles with R using lexRankr](https://adamspannbauer.github.io/2017/12/17/summarizing-web-articles-with-r/)
* [lexRankr & Twitter: find a user's most representative tweets](https://adamspannbauer.github.io/2017/03/09/lexrankr--twitter-find-a-users-most-representative-tweets/)
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