Import raw bytes as raw bytes in R

问题:

I have imported a string into R from a database. The db column type is BYTEA (Postgres). In order for me to use it as intended, it should be of type raw. Instead, it is of type character. I want to convert it to raw in the following sense:

The string representation is

\x1f8b080000000000

If I use charToRaw, it is converted to the array

5c 78 31 66 38 62 30 38 

Instead I need it to be the array

1f 8b 08 00 00 00 00 00

How do I acheive this.

Edit #1 Reply to Chris

library(RPostgreSQL)
conn <- dbConnect(dbDriver("PostgreSQL"), dbname = "somename",
                  host = "1.2.3.4", port = 5432,
                  user = "someuser", password = pw)
some_value <- dbGetQuery(conn, "select value from schema.key_value where key like '%somekey%' limit 1")

some_value$value
# [1] "\\x1f8b080000000000000

回答1:

This works for converting a single character string of the type you've described to a vector of raws.

## The string I think you're talking about
dat <- "\\x1f8b080000000000"
cat(dat, "\n")
## \x1f8b080000000000

## A function to convert one string to an array of raw
f <- function(x)  {
    ## Break into two-character segments
    x <- strsplit(x, "(?<=.{2})", perl=TRUE)[[1]]
    ## Remove the first element, "\\x"
    x <- x[-1]
    ## Complete the conversion
    as.raw(as.hexmode(x))
}

## Check that it works
f(dat)
##  [1] 1f 8b 08 00 00 00 00 00