The Ruby Way: Solutions and Techniques in Ruby Programming, Second Edition

5.3. Rounding Floating Point Values

Kirk: What would you say the odds are on our getting out of here?

Spock: It is difficult to be precise, Captain. I should say approximately 7824.7 to one.

—Star Trek, “Errand of Mercy”

If you want to round a floating point value to an integer, the method round will do the trick:

pi = 3.14159
new_pi = pi.round   # 3
temp = -47.6
temp2 = temp.round  # -48

Sometimes we want to round not to an integer but to a specific number of decimal places. In this case, we could use sprintf (which knows how to round) and eval to do this:

pi = 3.1415926535
pi6 = eval(sprintf("%8.6f",pi))  # 3.141593
pi5 = eval(sprintf("%8.5f",pi))  # 3.14159
pi4 = eval(sprintf("%8.4f",pi))  # 3.1416

Of course, this is somewhat ugly. Let’s encapsulate ...