subRaw?
Hi, Herv?:
On 7/19/2012 10:19 PM, Herv? Pag?s wrote:
Hi Spencer, On 07/19/2012 08:29 PM, Spencer Graves wrote:
Hello, All:
Do you know of any capability to substitute more then one byte in
an object of class Raw?
Consider the following:
> let4 <- paste(letters[1:4], collapse='') > (let4Raw <- charToRaw(let4))
[1] 61 62 63 64
> (let. <- sub('bc', '--', let4Raw))
[1] "61" "62" "63" "64"
> # no substitution
> (bc <- charToRaw('bc'))
[1] 62 63
> (ef <- charToRaw('ef'))
[1] 65 66
> (let. <- sub(bc, ef, let4Raw))
[1] "61" "65" "63" "64" Warning messages: 1: In sub(bc, ef, let4Raw) : argument 'pattern' has length > 1 and only the first element will be used 2: In sub(bc, ef, let4Raw) : argument 'replacement' has length > 1 and only the first element will be used
It makes no sense to use sub(), grep(), and family (i.e. all the stuff based on the regex code) *directly* on a raw vector because all these functions will start by coercing their 'x', 'text', 'pattern', 'replacement' args to character with as.character (if they are not already character). But the way as.character() operates on a raw vector won't give good results in that context. You'd rather do the coercion yourself first with rawToChar(), and coerce back the result with charToRaw():
> charToRaw(sub("bc", "--", rawToChar(let4Raw)))
[1] 61 2d 2d 64 IMO it would make much more sense that sub(), grep(), and family() raise an error than blindly try to coerce to character but these functions (like many functions in R) are too polite to tell the user s/he's doing something wrong.
Thanks for the reply.
It sounds like you agree that a function "subRaw" to facilitate
this would be useful. In my testing, charToRaw(sub(pattern,
replacement, rawToChar(x)) did NOT preserve binary codes that did not
match legitimate characters. I tried several things before finding one
that seemed to work.
Best Wishes,
Spencer
Cheers, H.
In this example, "b" was replaced by "e", but "bc" was not
replaced by "ef"? Do you know of any function to do this?
I ask, because I need it. I've written such a function, subRaw
for my own use. If I don't hear that another exists, I plan to add the
one I've written to the oro.dicom package.
Thanks,
Spencer
> sessionInfo()
R version 2.15.1 (2012-06-22) Platform: x86_64-pc-mingw32/x64 (64-bit) locale: [1] LC_COLLATE=English_United States.1252 [2] LC_CTYPE=English_United States.1252 [3] LC_MONETARY=English_United States.1252 [4] LC_NUMERIC=C [5] LC_TIME=English_United States.1252 attached base packages: [1] stats graphics grDevices utils datasets methods base