从数字数组中获取一个数字 [英] Get a number from an array of digits

问题描述

要将数字拆分为给定基数的数字，Julia 有 digits() 函数:

To split a number into digits in a given base, Julia has the digits() function:

julia> digits(36, base = 4)
3-element Array{Int64,1}:
 0
 1
 2

什么是反向操作?如果您有一个数字数组和底数，是否有一种 内置 方法可以将其转换为数字?我可以将数组打印为字符串并使用 parse()，但这听起来效率低下，也不适用于基数 > 10.

What's the reverse operation? If you have an array of digits and the base, is there a built-in way to convert that to a number? I could print the array to a string and use parse(), but that sounds inefficient, and also wouldn't work for bases > 10.

推荐答案

答案好像直接写在digits的文档里面:

The answer seems to be written directly within the documentation of digits:

help?> digits
search: digits digits! ndigits isdigit isxdigit disable_sigint

  digits([T<:Integer], n::Integer; base::T = 10, pad::Integer = 1)

  Return an array with element type T (default Int) of the digits of n in the given base,
  optionally padded with zeros to a specified size. More significant digits are at higher
  indices, such that n == sum([digits[k]*base^(k-1) for k=1:length(digits)]).

因此，对于您的情况，这将起作用:

So for your case this will work:

julia> d = digits(36, base = 4);

julia> sum([d[k]*4^(k-1) for k=1:length(d)])
36

并且上面的代码可以用点运算符缩短:

And the above code can be shortened with the dot operator:

julia> sum(d.*4 .^(0:(length(d)-1)))
36

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