Use of fread() from data.table causes R session to abort

Question

I am working on a project for a MOOC, and was tinkering around with the data.table package in RStudio. Use of the fread() function to import the data files initially worked fine:

fread("UCI HAR Dataset/features.txt")->features
fread("UCI HAR Dataset/test/y_test.txt")->ytest

However, when I tried to run the following line of code, I received a pop-up that said "R Session Aborted: R encountered a fatal error. The session was terminated."

fread("UCI HAR Dataset/test/X_test.txt")->xtest

I don't understand what the problem is. I checked the file names and paths to make sure I had correctly spelled and capitalized everything, and it all checks out. The equivalent code using read.table() works fine and does not cause R to abort. I also tried renaming the file to "x_test.txt", but the same issue occurred.

According to ?fread, only the function will only work with "regular delimited files." As far as I can tell, the file is a "regular delimited file", in that all rows have the same number of columns. There are no cells containing "NA" when I use read.table instead; I checked using anyNA(). Is there a quick way to determine whether a file is a delimited "regularly" or not? Is there something else about the original file that could be causing the problem?

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UPDATE

After further research and searching through the reported issues listed on the developer's github, I think that my problem lies in having two white spaces at the beginning of each row, which is discussed here. I am unsure why R aborted instead of giving me a warning. The latest development version of data.table (1.9.5) isn't causing the session to abort under the same conditions, though.

Answer 1

Although I do believe you should have contacted the package maintainer first for any situation where the R session was aborted (and it was not due to your mucking with C-code), I can offer a strategy for your last request which is not really specific to fread but I've found useful with regular-reads(). I'm going to assume that this is a comma separated file but if it;'s whitespace separated you could change the sep="," to sep="".

filcnts <- count.fields("UCI HAR Dataset/test/X_test.txt", sep=",")
table(filcnts)

That should be a single items table. If not, try switching parameters such as quote, sep, blank.lines.skip, or comment.char