有效地截断 Ruby Time 对象

Question

我正在尝试提出一种根据给定分辨率截断 Ruby Time 对象的有效方法。

class Time
  def truncate resolution
    t = to_a
    case resolution
    when :min   
      t[0] = 0
    when :hour
      t[0] = t[1] = 0
    when :day
      t[0] = t[1] = 0
      t[2] = 1
    when :month 
      t[0] = t[1] = 0
      t[2] = t[3] = 1
    when :week  
      t[0] = t[1] = 0
      t[2] = 1
      t[3] -= t[6] - 1
    when :year
      t[0] = t[1] = 0
      t[2] = t[3] = t[4] = 1
    end

    Time.local *t
  end
end

有谁知道实现相同任务的更快版本？

Answer 1

这已经在 Rails 的 ActiveSupport 库的Time extensions 中为您实现。查看change 方法，以及各种at_beginning_of_* 方法。

Answer 2

感谢你们俩。因为我不使用 Rails，所以我复制了代码来执行性能基准测试。

require 'benchmark'

class Time
  def truncate resolution
    t = to_a
    case resolution
    when :min   
      t[0] = 0
    when :hour
      t[0] = t[1] = 0
    when :day
      t[0] = t[1] = t[2] = 0
    when :week  
      t[0] = t[1] = t[2] = 0
      t[3] -= t[6] - 1
    when :month 
      t[0] = t[1] = t[2] = 0
      t[3] = 1
    when :year
      t[0] = t[1] = t[2] = 0
      t[3] = t[4] = 1
    end

    Time.local *t 
  end

  def truncate2 resolution
    opts = {}

    case resolution
    when :min   
      opts[:sec] = 0
    when :hour
      opts[:sec] = opts[:min] = 0
    when :day
      opts[:sec] = opts[:min] = opts[:hour] = 0
    when :week  
      opts[:sec] = opts[:min] = opts[:hour] = 0
      opts[:day] = wday - 1 if wday != 1
    when :month 
      opts[:sec] = opts[:min] = opts[:hour] = 0
      opts[:day] = 1
    when :year
      opts[:sec] = opts[:min] = opts[:hour] = 0
      opts[:day] = opts[:month] = 1
    end

    change opts 
  end

  def truncate3 resolution
    t = to_a
    if resolution == :week
      t[0] = t[1] = 0
      t[2] = 1
      t[3] -= t[6] - 1
    else
      len = [:sec, :min, :hour, :day, :month, :year].index(resolution)
      t.fill(0, 0, len)
      t.fill(1, 3, len-3)
    end

    Time.local *t
  end    

  def change opts 
    Time.local(
      opts[:year]  || year,
      opts[:month] || month,
      opts[:day]   || day,
      opts[:hour]  || hour,
      opts[:min]   || (opts[:hour] ? 0 : min),
      opts[:sec]   || ((opts[:hour] || opts[:min]) ? 0 : sec),
    )
  end
end

Resolutions = [:sec, :min, :hour, :day, :week, :month, :year]

# Correctness check.
puts Resolutions.map { |r| "#{r}: #{Time.now.truncate r}" } << "\n"
puts Resolutions.map { |r| "#{r}: #{Time.now.truncate2 r}" } << "\n"
puts Resolutions.map { |r| "#{r}: #{Time.now.truncate3 r}" } << "\n"

n = 100000
now = Time.now

Benchmark.bm(10) do |x|
  x.report("truncate") { n.times { Resolutions.each { |r| now.truncate  r } } }
  x.report("truncate2") { n.times { Resolutions.each { |r| now.truncate2 r } } }
  x.report("truncate3") { n.times { Resolutions.each { |r| now.truncate3 r } } }
end

Benchmark.bm(10) do |x|
  Resolutions.each do |unit| 
    x.report("#{unit}") { n.times { now.truncate unit } }
    x.report("#{unit}2") { n.times { now.truncate2 unit } }
    x.report("#{unit}3") { n.times { now.truncate3 unit } }
  end
end

结果如下：

sec: 2009-05-26 13:44:20 -0700
min: 2009-05-26 13:44:00 -0700
hour: 2009-05-26 13:00:00 -0700
day: 2009-05-26 00:00:00 -0700
week: 2009-05-25 00:00:00 -0700
month: 2009-05-01 00:00:00 -0700
year: 2008-12-31 23:00:00 -0800

sec: 2009-05-26 13:44:20 -0700
min: 2009-05-26 13:44:00 -0700
hour: 2009-05-26 13:00:00 -0700
day: 2009-05-26 00:00:00 -0700
week: 2009-05-01 00:00:00 -0700
month: 2009-05-01 00:00:00 -0700
year: 2009-01-01 00:00:00 -0800

sec: 2009-05-26 13:44:20 -0700
min: 2009-05-26 13:44:00 -0700
hour: 2009-05-26 13:00:00 -0700
day: 2009-05-26 00:00:00 -0700
week: 2009-05-25 01:00:00 -0700
month: 2009-05-01 00:00:00 -0700
year: 2008-12-31 23:00:00 -0800

                user     system      total        real
truncate    5.910000   0.020000   5.930000 (  5.947453)
truncate2   6.180000   0.020000   6.200000 (  6.232918)
truncate3   6.150000   0.020000   6.170000 (  6.253931)
                user     system      total        real
sec         0.720000   0.000000   0.720000 (  0.749040)
sec2        0.830000   0.010000   0.840000 (  0.863029)
sec3        0.800000   0.000000   0.800000 (  0.820477)
min         0.700000   0.000000   0.700000 (  0.709238)
min2        0.860000   0.010000   0.870000 (  0.860168)
min3        0.770000   0.000000   0.770000 (  0.795734)
hour        0.680000   0.000000   0.680000 (  0.705306)
hour2       0.850000   0.010000   0.860000 (  0.867235)
hour3       0.740000   0.000000   0.740000 (  0.746338)
day         0.720000   0.000000   0.720000 (  0.724324)
day2        0.890000   0.010000   0.900000 (  0.894312)
day3        0.780000   0.000000   0.780000 (  0.788007)
week        0.730000   0.000000   0.730000 (  0.736604)
week2       0.910000   0.000000   0.910000 (  0.910925)
week3       0.600000   0.000000   0.600000 (  0.611683)
month       0.720000   0.000000   0.720000 (  0.719515)
month2      0.880000   0.010000   0.890000 (  0.888045)
month3      0.780000   0.000000   0.780000 (  0.789726)
year        1.540000   0.010000   1.550000 (  1.565335)
year2       0.830000   0.000000   0.830000 (  0.849737)
year3       1.600000   0.010000   1.610000 (  1.644958)

似乎我的第一个截断版本仍然是最有效的，除了年份情况。不过，truncate 和 truncate3 在这一年有一个小怪癖。它显示为

2008-12-31 23:00:00 -0800

而不是

2009-01-01 00:00:00 -0700

有什么想法吗？

Answer 3

如果您不想要 Greg 建议的 ActiveSupport，我认为您可以这样做

t = to_a
if resolution==:week
  t[0] = t[1] = 0
  t[2] = 1
  t[3] -= t[6] - 1
else
  len = [:sec, :min, :hour, :day, :month, :year].index(resolution)
  t.fill(0, 0,len)
  t.fill(1, 3,len-3)
end
Time.local *t

不知道是不是更快...

Answer 4

您不必使用 Rails 来使用 ActiveSupport 好东西。除了想使用 1.day 或 3.minutes 或 Time.now.beginning__of__day 之类的东西之外，我还遇到了这个确切的问题p>

irb(main):001:0> require 'rubygems'
=> true
irb(main):002:0> require 'activesupport'
=> true
irb(main):003:0> 1.day
=> 1 day
irb(main):004:0> 3.minutes
=> 180 seconds
irb(main):005:0> Time.now.beginning_of_day
=> Sun Jun 28 00:00:00 -0400 2009
irb(main):006:0>