Question

OK, I admit that the title is a bit misleading. I’m braindead currently, so I may be missing something obvious here.

I’m working on R-powered webapp, and I’d like to pass certain parameters to read.table function – sep among others. Everything works like a charm if I’m passing single-byte characters as sep argument: ,, ;, |… but if I try to pass \t, I get an error:

invalid 'sep' value: must be one byte

of course, this happens because \t is actually escaped (\\t). Is there any chance that I can escape escapes, and pass it “as is” – i.e. a single byte string?

Answer 1

You need to write sep="\t" as the parameter to read.table.

In the case of a tab, it is the t that gets escaped. In other words, you are telling R that t doesn’t really mean t, but tab. If you escape the \, by using \\ then you are telling R that the \ doesn’t really mean escape but a literal \.

Here is some code illustrating the correct usage of sep="\t" in read.table. And just for the fun of it, I use textConnection to use a connection to write to and read from, rather than using a file on disk:

# Create a tab delimited file
zz <- textConnection("foo", "w")
write.table(matrix(1:12, ncol=3), file=zz, sep="\t")
close(zz)
foo

# The simple way:
tabsep <- "\t"

# The hard way, or if data was passed from a web app and you need to clean it
tabsep <- gsub("\\\\t", "\t", "\\t")


# Read a tab delimited file
zz <- textConnection(foo)
read.table(zz, sep=tabsep)
close(zz)

This produces the following output:

  V1 V2 V3
1  1  5  9
2  2  6 10
3  3  7 11
4  4  8 12