Decode string in hexadecimal notation
In R, which is an efficient way of converting a string encoded in hexadecimal form, for example "40414243"
to its equivalent characters, for example. "@ABC"
?
For example, the equivalent of this code:
library(stringr)
FromHexString <- function (hex.string) {
result <- ""
length <- str_length(hex.string)
for (i in seq(1, length, by=2)) {
hex.value <- str_sub(hex.string, i, i + 1)
char.code <- strtoi(hex.value, 16)
char <- rawToChar(as.raw(char.code))
result <- paste(result, char, sep="")
char
}
result
}
What produces:
> FromHexString("40414243")
[1] "@ABC"
While the above code works, it is inefficient at all using a lot of string concatenations.
So the question is how to write an idiomatic, efficient R function that does this operation .
Edit: my sample only works for ASCII encoding, not UTF-8 encoded byte arrays.
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Check if this is more efficient (for longer lines):
string <- "40414243"
intToUtf8(
strtoi(
do.call(
paste0,
as.data.frame(
matrix(
strsplit(string, split = "")[[1]],
ncol=2,
byrow=TRUE),
stringsAsFactors=FALSE)),
base=16L)
)
#[1] "@ABC"
Otherwise, you can look for a C / C ++ implementation.
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Modify your code to use lookup tables R example here . Your lookup table will have 255 values. Place them in a vector and get their values from that vector.
No: no other solution will beat this if you need to make a lot of conversions.
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If you don't want to use a lookup table (or just like codegolfing :-)), consider writing a vectorized version of something like:
bar <- unlist(strsplit(foo,'')) #separates input into individual elements
items <- sapply(1:(length(bar)/2),function(j)paste0(bar[(2*j-1):(2*j)],sep='',collapse=''))
followed by strtoi
or something else.
But even easier (hopefully ...) is
sapply(1:(nchar(foo)/2) function(j) substr(foo,(2*j-1),(2*j)))
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