What is the ruby expression "%.1f" and how does this round a decimal?

Question

I want to round a float with many decimal places, such as 2.638232371 down to one decimal place, such as 2.6.

I found this will do so:

"%.2f" % 1.93213
#=> 1.93

But what is "%.2f"? and is the result a string? I'd just like to understand how this works.

The precision can be variable, BTW. Try this: `sprintf('%.*f', 5, Math::PI)` — C. K. Young, Jul 16 '14 at 03:47

Yu Hao · Accepted Answer · 2014-07-17T00:35:44.040

4

It's the format string used by Kernel#sprintf.

The syntax of a format string is:

%[flags][width][.precision]type

%.2f means to use the floating-point format with 2 digits of precision.

edited Jul 17 '14 at 00:35

answered Jul 16 '14 at 03:42

Yu Hao

score 0 · Answer 2 · answered Jul 16 '14 at 03:43

0

Try this in irb and see for yourself whether or not the result is a String:

result = "%.2f" % 1.93213
result.class

As for what "%.2f" means, check out the sprintf docs

answered Jul 16 '14 at 03:43

Some Guy

`$ irb` `irb(main):001:0> result = "%.2f" % 1.93213` `=> "1.93"` `irb(main):002:0> result.class` `=> String` – GroundBeesAhh Jul 18 '14 at 02:00

2 Answers2