将基数为 2 的数字（带小数部分）转换为 R 中的基数为 10 的数字？

Question

如何在 R 中将 base2 数（带小数部分）转换为 base10 数？该数字也可以是负数。

例子：

from2to10(10100101) # "165"
from2to10(0) # "0"
from2to10(10100101.01) # "165.25"
from2to10(-10100101) # "-165"
from2to10(-10100101.01) # "-165.25"
from2to10(111101111.010111) # "495.359375"

Answer 1

编辑：我意识到我假设输入是character，这对我来说可能是一个错误的假设。我相信相信 R 来保存你所有的 0 和 1（考虑到 R FAQ 7.31）有点信任，但我会保持原样，除非/直到出现更好的情况。

---

这很有趣...不确定是否有处理非十进制浮点数的 R 函数，所以这里有一个 ...

#' Convert floating-point binary to decimal
#'
#' @param s 'character'
#' @return 'numeric'
#' @examples
#' tests <- c("10100101", "0", "10100101.01", "-10100101", "-10100101.01", "111101111.010111")
#' base2float(tests)
#' # [1]  165.0000    0.0000  165.2500 -165.0000 -165.2500  495.3594
base2float <- function(s, base = 2L) {
  # ensure the strings seem logical:
  # - start with "-", "+", or "[01]"
  # - zero or more "[01]"
  # - optional decimal "." (can easily change to "," for alternate reps)
  # - zero or more "[01]"
  stopifnot(all(grepl("^[-+]?[01]*\\.?[01]*$", s)))
  splits <- strsplit(s, "\\.")
  wholes <- sapply(splits, `[[`, 1L)
  wholes[wholes %in% c("", "-", "+")] <- paste0(wholes[wholes %in% c("", "-", "+")], "0")
  fracs <- sapply(splits, `[`, 2L)
  fracs[is.na(fracs)] <- "0"
  # because string-length is used in our calcs ...
  fracs <- gsub("0+$", "0", fracs)
  whole10 <- strtoi(wholes, base = base)
  frac10 <- strtoi(fracs, base = base) / (base^nchar(fracs))
  whole10 + sign(whole10)*frac10
}

Answer 2

library(cwhmisc) # int, frac
from2to10 <- function(n) {
SignOfNumber <- ""
if (n < 0) {
n <- abs(n)
SignOfNumber <- "-"}

nWhole <- int(n)
nWhole <- as.character(nWhole)

nFraction <- frac(n)
nFraction <- as.character(nFraction)

DecimalWhole   <- sapply(strsplit(nWhole, split=""), function(x) sum(as.numeric(x) * 2^(rev(seq_along(x) - 1))))

if (nFraction == 0) {
DecimalFraction <- ""
paste0(SignOfNumber, DecimalWhole)
} else { # Find decimal fraction part

part3 <- function(x, y, z) { eval(parse(text=(paste(x, y, z,sep="")))) }
y <- as.numeric(strsplit(substr(part3("\"",n,"\""), which(strsplit(part3("\"",n,"\""), "")[[1]]==".") + 1, nchar(part3("\"",n,"\""))),"")[[1]])
DecimalFraction <- sum(y * (0.5^(1:length(y))))
paste0(SignOfNumber, DecimalWhole + DecimalFraction)
}
}

from2to10(10100101) # "165"
from2to10(0) # "0"
from2to10(10100101.01) # "165.25"
from2to10(-10100101) # "-165"
from2to10(-10100101.01) # "-165.25"
from2to10(111101111.010111) # "495.359375"; numeric to string; exact conversion
base2float("111101111.010111") # 495.3594; string to numeric; conversion with rounding. (r2evans)