Number format

Ruby
1

Hi all,

I have a number, for example, 1.123456789. What is the Ruby way to
change it into whatever number of floating points such as 1.12,
1.123,1.1234568 or 1.12345679.

Thanks,

Li

2

You can use the number.round method, but this doesn’t take a number of
decimal places.

To round 1.234 to 1.23 use this code:
x = 1.234
x = x * 100 # -> 123.4
x = x.round -> 123
x = x / 100.0 => 1.23

At least, that’s the best method I can find from the Ruby docs…

Dan

3

On 12/4/06, Li Chen [email protected] wrote:

–
Posted via http://www.ruby-forum.com/.

It might be better to leave the precision alone until you print it, in
which case, you can print it with #sprintf or String#% or similar:

irb(main):001:0> ‘%.2f’ % 1.23456789
=> “1.23”
irb(main):002:0> ‘%.5f’ % 1.23456789
=> “1.23457”

4

On Mon, Dec 04, 2006 at 10:48:41AM +0900, Li Chen wrote:

Hi all,

I have a number, for example, 1.123456789. What is the Ruby way to
change it into whatever number of floating points such as 1.12,
1.123,1.1234568 or 1.12345679.

You could use facets:

% sudo gem install facets
% irb

irb(main):001:0> require 'rubygems'
=> true
irb(main):002:0> require 'facet/float/round_at'
=> true
irb(main):003:0> require 'facet/float/round_to'
=> true
irb(main):004:0> x = 1.123456789
=> 1.123456789
irb(main):005:0> x.round_at(3)
=> 1.123
irb(main):006:0> x.round_at(7)
=> 1.1234568
irb(main):007:0> x.round_at(100)
=> 1.123456789
irb(main):008:0> x.round_to(0.001)
=> 1.123
irb(main):009:0> x.round_to(0.000001)
=> 1.123457

enjoy,

-jeremy

5

Daniel F. wrote:

You can use the number.round method, but this doesn’t take a number of
decimal places.

To round 1.234 to 1.23 use this code:
x = 1.234
x = x * 100 # -> 123.4
x = x.round -> 123
x = x / 100.0 => 1.23

At least, that’s the best method I can find from the Ruby docs…

This is not a good idea. Because the number being manipulated is binary
but
the display is decimal, the multiplication and division steps will fail
on
some numbers – many, in fact – and those numbers will print more
decimal
places than was intended.

It’s better to retain the full binary resolution of a number internally,
and
only show certain decimal places while printing a number – don’t try to
truncate the number itself.

6

It might be better to leave the precision alone
until you print it, in
which case, you can print it with #sprintf or
String#% or similar:

irb(main):001:0> ‘%.2f’ % 1.23456789
=> “1.23”
irb(main):002:0> ‘%.5f’ % 1.23456789
=> “1.23457”

I think I prefer the suggestion.

Li