英文:
What's the difference between Float#floor and Float#to_i in Ruby?
问题
以下是翻译好的部分：
我正在学习Ruby，目前正在学习数字部分。据我理解，有五种方法（也许还有更多）可以将整数和浮点数相互强制转换：
Integer#to_f：强制转换为新的浮点数Float#ceil：四舍五入到最接近的整数Float#floor：向下舍入到最接近的整数Float#round：四舍五入到最接近的整数Float#to_i：截断到最接近的整数
“向下舍入”和“截断到最接近的整数”之间有什么区别？
当我进行测试时…
puts 34.4.to_i()
puts 34.4.floor()
…结果是相同的值：
34
34
英文:
I'm learning Ruby, and I'm currently in numbers. So as I understand it, there are five ways (perhaps more) to coerce integers and floats to each other:
Integer#to_f: Coerce to a new floatFloat#ceil: Round up to the nearest integerFloat#floor: Round down to the nearest integerFloat#round: Round to the nearest integerFloat#to_i: Truncate to the nearest integer
What's the difference between "rounding down" and "truncating" to the nearest integer?
When I tested it...
puts 34.4.to_i()
puts 34.4.floor()
... it resulted in the same values:
34
34
答案1
得分: 6
floor（无参数）返回小于或等于接收器的下一个整数。ceil（无参数）返回大于或等于接收器的下一个整数。to_i丢弃接收器的小数部分并返回整数部分。
| f | f.to_i | f.floor | f.ceil | f.round |
|---|---|---|---|---|
| 11.8 | 11 | 11 | 12 | 12 |
| 11.5 | 11 | 11 | 12 | 12 |
| 11.2 | 11 | 11 | 12 | 11 |
| 11.0 | 11 | 11 | 11 | 11 |
| -11.2 | -11 | -12 | -11 | -11 |
| -11.5 | -11 | -12 | -11 | -12 |
| -11.8 | -11 | -12 | -11 | -12 |
to_i 对正数的行为类似于 floor，对负数的行为类似于 ceil。
实际上，这就是 Float#to_i 在 numeric.c 中的实现方式：
static VALUE
flo_to_i(VALUE num)
{
double f = RFLOAT_VALUE(num);
if (f > 0.0) f = floor(f);
if (f < 0.0) f = ceil(f);
return dbl2ival(f);
}
还有 truncate，它的行为类似于 to_i，但接受可选的小数位数参数（类似于 floor、ceil 和 round）。
英文:
floor(without arguments) returns the next integer less than or equal to the receiverceil(without arguments) returns the next integer greater than or equal to the receiverto_idiscards the fractional part of the receiver and returns the integer part
| f | f.to_i | f.floor | f.ceil | f.round |
|---|---|---|---|---|
| 11.8 | 11 | 11 | 12 | 12 |
| 11.5 | 11 | 11 | 12 | 12 |
| 11.2 | 11 | 11 | 12 | 11 |
| 11.0 | 11 | 11 | 11 | 11 |
| -11.2 | -11 | -12 | -11 | -11 |
| -11.5 | -11 | -12 | -11 | -12 |
| -11.8 | -11 | -12 | -11 | -12 |
to_i behaves like floor for positive numbers and like ceil for negative numbers.
In fact, that's actually how Float#to_i is implemented in numeric.c:
static VALUE
flo_to_i(VALUE num)
{
double f = RFLOAT_VALUE(num);
if (f > 0.0) f = floor(f);
if (f < 0.0) f = ceil(f);
return dbl2ival(f);
}
There's also truncate which behaves like to_i but takes an optional number of digits (like floor, ceil, and round).
答案2
得分: 5
to_i 基本上只会从浮点数中移除小数部分，而 floor 会将其舍入到下一个较低的整数。这个差异在处理负浮点数时更容易看出来：
-34.4.floor
# => -35
-34.4.to_i
# => -34
值得注意的是 Float#round 支持不同的四舍五入模式。
:up或nil：向远离零的方向四舍五入：
2.5.round(half: :up) # => 3
3.5.round(half: :up) # => 4
(-2.5).round(half: :up) # => -3
:down：向零的方向四舍五入：
2.5.round(half: :down) # => 2
3.5.round(half: :down) # => 3
(-2.5).round(half: :down) # => -2
:even：向最后一个非零数字为偶数的候选值方向四舍五入：
2.5.round(half: :even) # => 2
3.5.round(half: :even) # => 4
(-2.5).round(half: :even) # => -2
英文:
The difference is that to_i basically only removes decimals from the float. Whereas float rounds down to the next lower integer. The difference is easier to see when dealing with negative floats:
-34.4.floor
#=> -35
-34.4.to_i
#=> -34
And it might be worth noting that Float#round supports different rounding modes.
`:up` or `nil`: round away from zero:
2.5.round(half: :up) # => 3
3.5.round(half: :up) # => 4
(-2.5).round(half: :up) # => -3
`:down`: round toward zero:
2.5.round(half: :down) # => 2
3.5.round(half: :down) # => 3
(-2.5).round(half: :down) # => -2
`:even`: round toward the candidate whose last nonzero digit is even:
2.5.round(half: :even) # => 2
3.5.round(half: :even) # => 4
(-2.5).round(half: :even) # => -2
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