Logo

Programming-Idioms

# 364 Calculate the magnitude symbol for a value
Calculate the SI (International System of Units) prefix, x, of value a.

For example, 'k', 'M', 'G', 'T', etc.

https://en.wikipedia.org/wiki/Metric_prefix
New implementation

Be concise.

Be useful.

All contributions dictatorially edited by webmasters to match personal tastes.

Please do not paste any copyright violating material.

Please try to avoid dependencies to third-party libraries and frameworks.

Other implementations 
#include <cmath>
#include <vector>
using namespace std;
struct units {
    double y;
    vector<char> a;
    units(int x) { y = log(x); }
    void add(char x) { a.push_back(x); }
    pair<int, char> get(int x) {
        int i (log(x) / y);
        return {i, a[i - 1]};
    }
};
units u {1'000};
for (char x : "kMGT") u.add(x);
pair p {u.get(a)};
a /= pow(1'000, p.first);
char x {p.second};
#include <cmath>
int y (log(a) / log(1'000));
a /= pow(1'000, y);
char x {"kMGT"[y - 1]};
import static java.lang.Math.log;
import static java.lang.Math.pow;
enum SI {
    k("kilo"),
    M("mega"),
    G("giga"),
    T("tera");
    String s;
    static double y = log(1_000);
    SI(String s) { this.s = s; }
    static SI get(double x) {
        int y = (int) (log(x) / SI.y);
        return values()[y - 1];
    }
}
SI si = SI.get(a);
a /= pow(1_000, si.ordinal() + 1);
String x = si.name();
import static java.lang.Math.log;
import static java.lang.Math.pow;
int y = (int) (log(a) / log(1_000));
a /= pow(1_000, y);
char x = "kMGT".charAt(y - 1);
function GetSIPrefix(AValue: Double): string;
const
  SIPrefixes: array[1..24] of String = ('Q','R','Y', 'Z','E','P','T','G','M','K','H','D','','d','c','m','µ','mc','n','p','f','a','z','y');
  SIFactors:  array[1..24] of Double = (1E+30,1E+27,1E+24, 1E+21, 1E+18, 1E+15, 1E+12, 1E+9, 1E+6, 1E+3,1E+2,1E+1,1,1E-1,1E-2,
var
  i: Integer;
begin
  Result := '';
  for i := 1 to 24 do
  begin
    if (Abs(AValue) >= SIFactors[i]) then
    begin
      Exit(SIPrefixes[i]);
    end;
  end;
end;
from enum import IntEnum, nonmember
from math import log
class Units(IntEnum):
    b_ = nonmember(1_000)
    k = 'kilo'
    M = 'mega'
    G = 'giga'
    T = 'tera'
    def __new__(_, x):
        y = len(_._member_map_) + 1
        y = _.b_ ** y
        i = int.__new__(_, y)
        i.x, i._value_ = x, y
        return i
    __str__ = lambda _: _.x
    @classmethod
    def parse(_, x):
        y = int(log(x, _.b_))
        return [*_][y - 1]
u = Units.parse(a)
s = f'{a / u} {u}bytes ({u.name}B)'
from math import log
y = int(log(a, 1_000))
a /= 1_000 ** y
x = 'kMGT'[y - 1]
from math import log
from string import printable
def f(x, s=printable, b=10):
    m = lambda _, x: int.__new__(_, x)
    n = lambda _: _.__class__.__name__
    d = {'__new__': m, '__str__': n}
    y = int(log(x, b))
    x = type(s[y - 1], (int,), d)
    return x(b ** y)
u = f(a, 'kMGT', 1_000)
s = f'{a / u} {u}B'
from math import log
from string import printable
def m(_, s=printable, b=10):
    _.b = b
    m = lambda _, x: int.__new__(_, x)
    n = lambda _: _.__class__.__name__
    d = {'__new__': m, '__str__': n}
    for y, x in enumerate(s, 1):
        x = type(x, (int,), d)
        _.append(x(b ** y))
n = lambda _, x: _[int(log(x, _.b)) - 1]
d = {'__init__': m, 'parse': n}
Units = type('Units', (list,), d)
u = Units('kMGT', 1_000)
u = u.parse(a)
s = f'{a / u} {u}B'
x =  case a
  when 1e3... 1e6 ; "k"
  when 1e6... 1e9 ; "M"
  when 1e9... 1e12; "G"
  when 1e12...1e15; "T"
  else ""
end

Preview