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Kay Cichini (MSc, Biology), Nature Protection Expert, Tyrol/Austria. I'm author of theBioBucket-Blog, where I share examples for data management, data processing, statistical analysis and report generation using the R-Software. Kay is a DZone MVB and is not an employee of DZone and has posted 28 posts at DZone. You can read more from them at their website. View Full User Profile

Reading and Text Mining a PDF-File in R

09.29.2012
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Here is an R-script that reads a PDF-file to R and does some text mining with it:

# here is a pdf for mining
url <- "http://www.noisyroom.net/blog/RomneySpeech072912.pdf"
dest <- tempfile(fileext = ".pdf")
download.file(url, dest, mode = "wb")

# set path to pdftotxt.exe and convert pdf to text
exe <- "C:\\Program Files\\xpdfbin-win-3.03\\bin32\\pdftotext.exe"
system(paste("\"", exe, "\" \"", dest, "\"", sep = ""), wait = F)

# get txt-file name and open it
filetxt <- sub(".pdf", ".txt", dest)
shell.exec(filetxt); shell.exec(filetxt) # strangely the first try always throws an error..

# do something with it, i.e. a simple word cloud
library(tm)
library(wordcloud)
library(Rstem)

txt <- readLines(filetxt) # don't mind warning..

txt <- tolower(txt)
txt <- removeWords(txt, c("\\f", stopwords()))

corpus <- Corpus(VectorSource(txt))
corpus <- tm_map(corpus, removePunctuation)
tdm <- TermDocumentMatrix(corpus)
m <- as.matrix(tdm)
d <- data.frame(freq = sort(rowSums(m), decreasing = TRUE))

# Stem words
d$stem <- wordStem(row.names(d), language = "english")

# and put words to column, otherwise they would be lost when aggregating
d$word <- row.names(d)

# remove web address (very long string):
d <- d[nchar(row.names(d)) < 20, ]

# aggregate freqeuncy by word stem and
# keep first words..
agg_freq <- aggregate(freq ~ stem, data = d, sum)
agg_word <- aggregate(word ~ stem, data = d, function(x) x[1])

d <- cbind(freq = agg_freq[, 2], agg_word)

# sort by frequency
d <- d[order(d$freq, decreasing = T), ]

# print wordcloud:
wordcloud(d$word, d$freq)

# remove files
file.remove(dir(tempdir(), full.name=T)) # remove files

 

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