How to truncate float number after dot?

Ruby
1

Hi,

How to truncate float number after dot? I suppose it would be easy.

Thank in advance
MT

2

On 7/26/07, Marcin T. [email protected] wrote:

Hi,

How to truncate float number after dot? I suppose it would be easy.

Thank in advance

19.84.round #=> big brother is watching you

3

On 7/26/07, Marcin T. [email protected] wrote:

Hi,

How to truncate float number after dot? I suppose it would be easy.

Thank in advance
MT

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

irb(main):001:0> 12.68.floor
=> 12
irb(main):002:0> 12.68.ceil
=> 13

Pat

4

2007/7/26, Pat M. [email protected]:

irb(main):001:0> 12.68.floor
=> 13
irb(main):004:0> 12.38.round
=> 12

12.38.to_i

robert

5

On 7/26/07, Pat M. [email protected] wrote:

irb(main):001:0> 12.68.floor
=> 12
irb(main):002:0> 12.68.ceil
=> 13

Pat

Gah, I forgot the all important round!

irb(main):003:0> 12.68.round
=> 13
irb(main):004:0> 12.38.round
=> 12

Pat

6

I didn’t mean to truncate all. But i.e. to round to several places after
dot.

7

2007/7/26, Marcin T. [email protected]:

I didn’t mean to truncate all. But i.e. to round to several places after
dot.

Usually it’s better to calculate with full precision and round when
printing, e.g. using printf of

irb(main):022:0> “%4.1f” % 1.0
=> " 1.0"
irb(main):023:0> “%4.1f” % 1.04
=> " 1.0"
irb(main):024:0> “%4.1f” % 1.05
=> " 1.1"

Kind regards

robert

8

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Marcin T. wrote:

How to truncate float number after dot? I suppose it would be easy.

Rounding to a certain number of digits works as follows:

Let n be the number of digits following the decimal point you want to
obtain. Then

  1. Multiply the number by 10 to the power n (i.e. by 10.0 ** n)
  2. Round the number (i.e. use Float#round)
  3. Divide the result by 10 to the power n

The latter can either be done by division by 10.0 ** n or by
multiplication by 0.1 ** n.

But as Robert K. already noted: It rarely makes sense to actually
round numbers. It usually makes more sense to compute with the available
precision and limit the output to the wanted number of digits.

Anyway, sometimes it makes sense. For example if you are required by law
to round intermediate calculation results to a certain amount of digits.
But in such cases one should not at all use floating point numbers for
the computations. One would rather use integers, fixed-point arithmetics
(as e.g. supported by COBOL) or the Decimal data type from Microsoft’s
Common Type System (e.g. supported by C#).

Josef ‘Jupp’ Schugt

Blog available at http://www.mynetcologne.de/~nc-schugtjo/blog/
PGP key with id 6CC6574F available at http://wwwkeys.de.pgp.net/
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