Error in reading files in R - r

Question

I'm a newcomer in the R community. Coding my first programs I've faced with a silly problem! When trying to read an RDS file with the following code:
tweets <- readRDS("RDataMining-Tweets-20160212.rds")
the following error will arise.
Error in gzfile(file, "rb") : cannot open the connection
In addition: Warning message:
In gzfile(file, "rb") :
cannot open compressed file 'RDataMining-Tweets-20160212.rds', probable reason 'No such file or directory'
What's the problem here?

Answer 1

Since we don't have access to your file, it'll be difficult to really know for sure, so let me give you some examples of what other types files might give you.
First, some files:
ctypes <- list(FALSE, 'gzip', 'bzip2', 'xz')
saverds_names <- sprintf('saveRDS_%s.rds', ctypes)
save_names <- sprintf('save_%s.rda', ctypes)
ign <- mapply(function(fn,ct) saveRDS(mtcars, file=fn, compress=ct),
saverds_names, ctypes)
ign <- mapply(function(fn,ct) save(mtcars, file=fn, compress=ct),
save_names, ctypes)
str(lapply(saverds_names, function(fn) system2("file", fn, stdout=TRUE)))
# List of 4
# $ : chr "saveRDS_FALSE.rds: data"
# $ : chr "saveRDS_gzip.rds: gzip compressed data, from HPFS filesystem (OS/2, NT)"
# $ : chr "saveRDS_bzip2.rds: bzip2 compressed data, block size = 900k"
# $ : chr "saveRDS_xz.rds: XZ compressed data"
str(lapply(save_names, function(fn) system2("file", fn, stdout=TRUE)))
# List of 4
# $ : chr "save_FALSE.rda: data"
# $ : chr "save_gzip.rda: gzip compressed data, from HPFS filesystem (OS/2, NT)"
# $ : chr "save_bzip2.rda: bzip2 compressed data, block size = 900k"
# $ : chr "save_xz.rda: XZ compressed data"
A common (unix-y) utility is file, which uses file signatures to determine probable file type. (If you are on windows, it is usually installed with Rtools, so look for it there. If Sys.which("file") is empty, then look around for where you have Rtools installed, for something like c:\Rtools\bin\file.exe.)
Sys.which('file')
# file
# "c:\\Rtools\\bin\\file.exe"
With this, let's see what file thinks these files are likely to be:
str(lapply(saverds_names, function(fn) system2("file", fn, stdout=TRUE)))
# List of 4
# $ : chr "saveRDS_FALSE.rds: data"
# $ : chr "saveRDS_gzip.rds: gzip compressed data, from HPFS filesystem (OS/2, NT)"
# $ : chr "saveRDS_bzip2.rds: bzip2 compressed data, block size = 900k"
# $ : chr "saveRDS_xz.rds: XZ compressed data"
str(lapply(save_names, function(fn) system2("file", fn, stdout=TRUE)))
# List of 4
# $ : chr "save_FALSE.rda: data"
# $ : chr "save_gzip.rda: gzip compressed data, from HPFS filesystem (OS/2, NT)"
# $ : chr "save_bzip2.rda: bzip2 compressed data, block size = 900k"
# $ : chr "save_xz.rda: XZ compressed data"
Helps a little. If your does not return one of these four strings, then you are likely looking at a corrupted file (or mis-named, i.e., not really an .rds format that we are expecting).
If it does return one of them, though, know that readRDS (the first four) and load (last four) will automatically determine the compress= argument to use, which means that the file is most likely corrupt (or some other form of compressed data; again, likely mis-named).
In contrast, some other file types return these:
system2("file", "blank.accdb")
# blank.accdb: raw G3 data, byte-padded
system2("file", "Book1.xlsx")
# Book1.xlsx: Zip archive data, at least v2.0 to extract
system2("file", "Book1.xls")
# Book1.xls: OLE 2 Compound Document
system2("file", "j.fra.R") # code for this answer
# j.fra.R: ASCII text, with CRLF line terminators
(The with CRLF is a windows-y thing. *sigh*) The last one also will also be the case for CSV and similar text-based tabular files, etc.
#divibisan's suggestion that the file could be corrupt is the most likely culprit, in my mind, but it might give different output:
file.size(saverds_names[1])
# [1] 3798
head(readRDS(rawConnection(readBin(saverds_names[1], what=raw(1)))), n=2)
# mpg cyl disp hp drat wt qsec vs am gear carb
# Mazda RX4 21 6 160 110 3.9 2.620 16.46 0 1 4 4
# Mazda RX4 Wag 21 6 160 110 3.9 2.875 17.02 0 1 4 4
but incomplete data from truncated files looks different: I truncated the files (externally with dd), and the error I received as "Error in readRDS: error reading from connection\n".
Looking at the source for R, that error string is only present in R_gzread, suggesting that R thinks the file is compressed with "gzip" (which is the default, perhaps because it could not positively identify any other obvious compression method).
This isn't much of an answer, but it might give you some appreciation for what could be wrong. The bottom line, unfortunately, is that it is highly unlikely to be able to recover any data from a corrupted.

Answer 2

Try to open the file in this way, avoiding any kind of possible problem related to the file path:
tweets <- readRDS(file.choose())
An interactive window will be open and you will be able to select your file.

Answer 3

There are two rds files at the website that supports the book you are following:
http://www.rdatamining.com/data/
One of them is named: RDataMining-Tweets-20160203.rds and the other is named: RDataMining-Tweets-20160212.rds. I suspect you put them in a "downloads" folder using your browser and it happens to be different folder than the one that you will see if you execute:
getwd()
You should try re-downloading from that website and checking the file locations.
You can get a listing of files in your current working directory with:
list.files()
Make sure that the file name appears in that output.
If that proves difficult, then this also should succeed:
tweets2 <- readRDS( url("http://www.rdatamining.com/data/RDataMining-Tweets-20160212.rds?attredirects=0&d=1") )
str(tweets2) # should be a complex and long output
The url function creates a "connection" that can be used to download RDS files

Answer 4

First check your working directory by getwd(). Check whether the file you want to red in this directory or not. If not use setwd(dir=<#pathwhere you want to change it>).
i think you should not use readRDS in double quotes as extension .rds is already there. Instead use with file equivalent as readRDS(File="RDataMining-Tweets-20160212.rds")

Answer 5

Chuckle - I recognise that data file name...
You appear to be using the reference data from Yanchang Zhao's presentation on "Text Mining with R", the data set can be downloaded via the author's website [http://www.rdatamining.com/data] using this link - [RDataMining-Tweets-20160203.rds]
Looking at the error, as Devyani Balyan states the file you are trying to load is likely not in your working directory. The code examples generally put the data file in a <project>\data structure. Yanchang in his examples follows this heuristic.
My recommendation is you get a copy of a good R book to help get you started. My personal recommendation would be "The R Book" by Michael J. Crawley.
Here is a working code example, I hope it helps you progress:
Code Example
# used to load multiple R packages at once
# and or install them.
ipak <- function(pkg){
new.pkg <- pkg[!(pkg %in% installed.packages()[, "Package"])]
if (length(new.pkg))
install.packages(new.pkg, dependencies = TRUE)
sapply(pkg, require, character.only = TRUE)
}
# Load twitterR Package
packages <- c("twitteR")
ipak(packages)
# Load Example dataset from the website
url <- "http://www.rdatamining.com/data/RDataMining-Tweets-20160212.rds"
destfile = "RDataMining-Tweets-20160212.rds"
# Download into the current directory for simplicity
# Normally I would recommend saving to <project>/data
# Check if file exists if not download it...
if (!file.exists(destfile)) {
download.file(url, destfile)
}
## load tweets into R
tweets <- readRDS(destfile)
head(tweets, n = 3)
Console output
> ipak <- function(pkg){
+ new.pkg <- pkg[!(pkg %in% installed.packages()[, "Package"])]
+ if (length(new.pkg))
+ install.packages(new.pkg, dependencies = TRUE)
+ sapply(pkg, require, character.only = TRUE)
+ }
> # Load twitterR Package
> packages <- c("twitteR")
> ipak(packages)
twitteR
TRUE
> url <- "http://www.rdatamining.com/data/RDataMining-Tweets-20160212.rds"
> destfile = "RDataMining-Tweets-20160212.rds"
> # Check if file exists if not download it...
> if (!file.exists(destfile)) {
+ download.file(url, destfile)
+ }
> ## load tweets into R
> tweets <- readRDS(destfile)
> head(tweets, n = 3)
[[1]]
[1] "RDataMining: A Twitter dataset for text mining: #RDataMining Tweets extracted on 3 February 2016. Download it at **********"
[[2]]
[1] "RDataMining: Vacancy of Data Scientist – Healthcare Analytics, Adelaide, Australia\n***********"
[[3]]
[1] "RDataMining: Thanks to all for your ongoing support to ******** 3. Merry Christmas and Happy New Year!"

Answer 6

It seems your working directory is not properly set.
See which directory you downloaded the file in and copy the path.
Use the command setwd('Your/path/here') and then it should work. Just remember to change the orientation of your slashes (from '\' to '/').