Question

我有以下哈希值：

{
  "01/01"=>{:a=>0, :b=>2},
  "01/05"=>{:a=>1, :b=>0},
  "31/08"=>{:a=>26, :b=>32},
  "01/09"=>{:a=>2, :b=>9},
  "02/09"=>{:a=>0, :b=>3},
  "04/09"=>{:a=>0, :b=>4},
  "06/09"=>{:a=>0, :b=>26},
  "07/09"=>{:a=>0, :b=>2},
  "06/10"=>{:a=>0, :b=>1},
  "07/11"=>{:a=>0, :b=>1}
}

该哈希有10个条目，但我只需要显示7个即可。我怎样才能只获得7个条目来使用这些值？

谢谢。

Answer 1

前7个元素

您可以在转换为数组的哈希上使用Array#slice，然后再转换回哈希。这是一个示例：

x = {
  "01/01"=>{:a=>0, :b=>2},
  "01/05"=>{:a=>1, :b=>0},
  "31/08"=>{:a=>26, :b=>32},
  "01/09"=>{:a=>2, :b=>9},
  "02/09"=>{:a=>0, :b=>3},
  "04/09"=>{:a=>0, :b=>4},
  "06/09"=>{:a=>0, :b=>26},
  "07/09"=>{:a=>0, :b=>2},
  "06/10"=>{:a=>0, :b=>1},
  "07/11"=>{:a=>0, :b=>1}
}

y = x.to_a.slice(0,7).to_h

然后y是

{
  "01/01"=>{:a=>0, :b=>2},
  "01/05"=>{:a=>1, :b=>0},
  "31/08"=>{:a=>26, :b=>32},
  "01/09"=>{:a=>2, :b=>9},
  "02/09"=>{:a=>0, :b=>3},
  "04/09"=>{:a=>0, :b=>4},
  "06/09"=>{:a=>0, :b=>26}
}

哈希还具有切片方法（至少在2.5.1中），但是需要提供从哈希中进行切片的键。如果您事先知道按键，则可以：

y = x.slice("01/01", "01/05", "31/08", "01/09", "02/09", "04/09", "06/09")

对于y，结果相同。

Hash#slice文档：https://ruby-doc.org/core-2.5.1/Hash.html#method-i-slice

最后7个元素

您可以在转换为数组的哈希上使用Array#last，然后再转换回哈希。这是一个示例：

x = {
  "01/01"=>{:a=>0, :b=>2},
  "01/05"=>{:a=>1, :b=>0},
  "31/08"=>{:a=>26, :b=>32},
  "01/09"=>{:a=>2, :b=>9},
  "02/09"=>{:a=>0, :b=>3},
  "04/09"=>{:a=>0, :b=>4},
  "06/09"=>{:a=>0, :b=>26},
  "07/09"=>{:a=>0, :b=>2},
  "06/10"=>{:a=>0, :b=>1},
  "07/11"=>{:a=>0, :b=>1}
}

y = x.to_a.last(7).to_h

然后y是

{
  "01/09"=>{:a=>2, :b=>9},
  "02/09"=>{:a=>0, :b=>3},
  "04/09"=>{:a=>0, :b=>4},
  "06/09"=>{:a=>0, :b=>26},
  "07/09"=>{:a=>0, :b=>2},
  "06/10"=>{:a=>0, :b=>1},
  "07/11"=>{:a=>0, :b=>1}
}

Answer 2

不太清楚，但这也许可以帮上忙。

要获取前七个values：

h.values.first(7) # or h.values.take(7)
# => [{:a=>0, :b=>2}, {:a=>1, :b=>0}, {:a=>26, :b=>32}, {:a=>2, :b=>9}, {:a=>0, :b=>3}, {:a=>0, :b=>4}, {:a=>0, :b=>26}]

要获取前七个keys：

h.keys.first(7) # => ["01/01", "01/05", "31/08", "01/09", "02/09", "04/09", "06/09"]

或者仅获得first七个元素，如注释中已经指出的那样：

h.first(7).to_h
# {"01/01"=>{:a=>0, :b=>2}, "01/05"=>{:a=>1, :b=>0}, "31/08"=>{:a=>26, :b=>32}, "01/09"=>{:a=>2, :b=>9}, "02/09"=>{:a=>0, :b=>3}, "04/09"=>{:a=>0, :b=>4}, "06/09"=>{:a=>0, :b=>26}}

编辑：从头到尾获取最后七个

h.values.last(7).reverse # => [{:a=>0, :b=>1}, {:a=>0, :b=>1}, {:a=>0, :b=>2}, {:a=>0, :b=>26}, {:a=>0, :b=>4}, {:a=>0, :b=>3}, {:a=>2, :b=>9}]

Answer 3

您可以将Hash#select与计数器一起使用。

h = {
  "01/01"=>{:a=>0, :b=>2},
  "01/05"=>{:a=>1, :b=>0},
  "31/08"=>{:a=>26, :b=>32},
  "01/09"=>{:a=>2, :b=>9},
  "02/09"=>{:a=>0, :b=>3},
  "04/09"=>{:a=>0, :b=>4},
  "06/09"=>{:a=>0, :b=>26},
  "07/09"=>{:a=>0, :b=>2},
  "06/10"=>{:a=>0, :b=>1},
  "07/11"=>{:a=>0, :b=>1}
}

n = 7
h.select { (n-=1) >= 0 }
  #=> {"01/01"=>{:a=>0, :b=>2},
  #    "01/05"=>{:a=>1, :b=>0},
  #    "31/08"=>{:a=>26, :b=>32},
  #    "01/09"=>{:a=>2, :b=>9},
  #    "02/09"=>{:a=>0, :b=>3},
  #    "04/09"=>{:a=>0, :b=>4},
  #    "06/09"=>{:a=>0, :b=>26}}

从哈希条目获取范围

3 个答案: