How do I get a floating point number as a string without the exponent notation?

Question

How do I get a floating point number as a string without the exponent notation, that is, a number that ends in "e-10" or similar? I discovered to_s returns the number with the exponent notation.

ms = 1457000.0000000002 % 1000 # => 2.3283064365386963e-10
ms.to_s                        # => "2.3283064365386963e-10"

I would like to get "0.0000000002", but I don't get it right.

If I use my example above and evaluate "%f" % ms, I get "0.000000", which is much different from "0.0000000002".

Possible duplicate of [Ruby: Controlling printing in scientific notation](https://stackoverflow.com/questions/1189618/ruby-controlling-printing-in-scientific-notation) — moveson, Sep 25 '17 at 22:47
That solution doesn't wokr for me, tho. If you use my example above and run "%f" % ms, you get "0.000000", which is much different than "0.0000000002". — , Sep 25 '17 at 22:57
Well, technically, it's not *much* different, but may not reflect the accuracy you want. — Dave Newton, Sep 25 '17 at 23:18
_"I would like to get 0.0000000002"_ – why do you want 10 decimal places and not 12 or 15 or 32? — Stefan, Oct 16 '17 at 11:59

score 2 · Answer 1 · answered Sep 25 '17 at 23:41

2

I think it'd still work if you specify the number of decimal places (DP) %f. Take your example for instance, the output is an exponent of e-10 thus would be accurate if you specify the DP to 10. Here's a specific:

ms = 1457000.0000000002
secs, ms = ms.divmod(1000)
my_answer = '%.10f' % ms

Your output will be => "0.0000000002"

answered Sep 25 '17 at 23:41

Ian Shiundu

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Thanks. What if I don't know the number of decimal places in advance? – Sep 26 '17 at 00:02

score 0 · Answer 2 · answered Sep 27 '17 at 20:20

This appears to be a duplicate of this issue:

Force Ruby to not output a float in standard form / scientific notation / exponential notation

You can use sprintf to print the formatted number:

ms = 1457000.0000000002
sprintf("%.10f", ms)
 => "1457000.0000000002"

It's important to note that floating point numbers are not perfectly precise - so if you tell sprintf to display more digits, say 16, you will see this imprecision:

sprintf("%.16f", ms)
=> "1457000.0000000002328306"

A trick for forcing the precision is to use to_r to convert the value to a Rational:

ms = '1457000.0000000002'.to_r
=> (7285000000000001/5000000000)
sprintf("%.16f", ms)
=> "1457000.0000000002000000"

How do I get a floating point number as a string without the exponent notation?

2 Answers2