Exponential notation is inaccurate

Question

I imported a dataset that contains large numbers that were automatically converted to exponential notation. Since I had to see the full number, I used the options (scipen = 999). I found that the imported number was not equal to the original number from the dataset. For example, 5765949338897345178 has been changed to 5765949338897345536.

How can it be that these numbers do not match? The strange thing is that when I use: which (dim_alias1 $ id == 5765949338897345536) and which (dim_alias1 $ id == 5765949338897345178), it returns the same number. How is this possible?

Answer 1

id, . .

:

dat <- data.frame(id=12345, x=1)
write.table(dat, tmp <- tempfile())
dat2 <- read.table(tmp, colClasses = c(id="character"))
str(dat2)

#'data.frame':  1 obs. of  2 variables:
# $ id: chr "12345"
# $ x : int 1