如何按升序对ruby数组进行排序，但最后保持为零

Question

I am trying to sort a Ruby array with the following function

@prices = @item.prices.sort { |x,y| x.total <=> y.total }

Which orders from the lowest to the highest cost. However some products have a total of 0.00 and I want them to appear last rather than at the top.

I have tried a few things but would like some way to modify this block to sort zero at the bottom but keep the rest in ascending order.

Thanks.

Answer 1

试试这个，我认为它正在按你的要求做：

@prices = @item.prices.sort {|a,b| a.total==0 ? 1 : b.total==0 ? -1 : a.total<=>b.total}

Answer 2

prices = [0, 1, 2, 0,4, 3]
prices = prices.sort_by do |price|
  [
    if price == 0
      1
    else
      0
    end,
    price
  ]
end
p prices
# => [1, 2, 3, 4, 0, 0]

The trick here is that arrays are compared by comparing their first elements, but if those elements are equal, then by comparing their next elements, and so on. So having the sort_by block yield an array lets you determine primary sort order, secondary sort order, and so on in a clean manner.

Answer 3

Just for the record:

>> a = [0, 1, 3, 0, 2, 5, 0, 9]
=> [0, 1, 3, 0, 2, 5, 0, 9]
>> a.sort_by { |x| x.zero? ? Float::MAX : x }
=> [1, 2, 3, 5, 9, 0, 0, 0]

On most platforms 1.0/0 will evaluate to Infinity , so you can also use this instead of Float::MAX :

>> b = [1,4,2,0,5,0]
=> [1, 4, 2, 0, 5, 0]
>> Inf = 1.0/0
=> Infinity
>> b.sort_by { |x| x.zero? ? Inf : x }
=> [1, 2, 4, 5, 0, 0]

Answer 4

So devise a comparator to do that ...

if x.total == 0
  # always consider 0 "largest" and no 0 can be larger than another
  # (make sure 0.0 is 0 and not a number really close to 0)
  # perhaps x or y should be first for other reasons as well?
  1
else
  # otherwise lower to higher as normal
  x.total <=> y.total
end

Or without comments:

foo.sort {|x, y| if x.total == 0 then 1 else x.total <=> y.total end}

Happy coding.

Answer 5

This would feel less hacky and less write-only to me:

prices = prices.sort_by do |price| 
  zero_status = price.zero? ? 1 : 0
  [zero_status, price]
end

because it's an idiomatic way of sorting something by two criteria, which is what you're doing here.