[R] Memory usage in R grows considerably while calculating word frequencies

[arun]

HI,

In the previous email, I forgot to add unlist().
With four paragraphs,
sapply(strsplit(txt1," "),length)
#[1] 4850 9072 6400 2071


#Your code:
system.time({
txt1<-tolower(scan("text_file","character",sep="\n")) 
pattern <- "(\\b[A-Za-z]+\\b)"
match <- gregexpr(pattern,txt1)
words.txt <- regmatches(txt1,match)
words.txt<-unlist(words.txt)
words.txt<-table(words.txt,dnn="words")
words.txt<-sort(words.txt,decreasing=TRUE)
words.txt<-paste(names(words.txt),words.txt,sep="\t")
cat("Word\tFREQ",words.txt,file="frequencies",sep="\n")
})

#Read 4 items
#   user  system elapsed 
# 11.781   0.004  11.799 


#Modified code:
system.time({
txt1<-tolower(scan("text_file","character",sep="\n")) 
 words.txt<-sort(table(unlist(strsplit(tolower(txt1),"\\s"))),decreasing=TRUE)
 words.txt<-paste(names(words.txt),words.txt,sep="\t")
 cat("Word\tFREQ",words.txt,file="frequencies",sep="\n") 
})
#Read 4 items
 #user  system elapsed 
 # 0.036   0.008   0.043 


A.K.




----- Original Message -----
From: mcelis <mcelis at lightminersystems.com>
To: r-help at r-project.org
Cc: 
Sent: Monday, September 24, 2012 7:29 PM
Subject: [R] Memory usage in R grows considerably while calculating word frequencies

I am working with some large text files (up to 16 GBytes).  I am interested
in extracting the words and counting each time each word appears in the
text. I have written a very simple R program by following some suggestions
and examples I found online.  

If my input file is 1 GByte, I see that R uses up to 11 GBytes of memory
when executing the program on
a 64-bit system running CentOS 6.3. Why is R using so much memory? Is there
a better way to do this that will
minimize memory usage.

I am very new to R, so I would appreciate some tips on how to improve my
program or a better way to do it.

R program:
# Read in the entire file and convert all words in text to lower case
words.txt<-tolower(scan("text_file","character",sep="\n"))

# Extract words
pattern <- "(\\b[A-Za-z]+\\b)"
match <- gregexpr(pattern,words.txt)
words.txt <- regmatches(words.txt,match)

# Create a vector from the list of words
words.txt<-unlist(words.txt)

# Calculate word frequencies
words.txt<-table(words.txt,dnn="words")

# Sort by frequency, not alphabetically
words.txt<-sort(words.txt,decreasing=TRUE)

# Put into some readable form, "Name of word" and "Number of times it
occurs"
words.txt<-paste(names(words.txt),words.txt,sep="\t")

# Results to a file
cat("Word\tFREQ",words.txt,file="frequencies",sep="\n")



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