排序时忽略nil个元素

Question

For sorting such struct I implemented three methods:

type Event struct {
    timeEnd interface{}
    size float64
}

func (s ByTime) Len() int {
    return len(s)
}
func (s ByTime) Swap(i, j int) {
    s[i], s[j] = s[j], s[i]
}

Sometimes not all Events.timeEnd are initialized and I want to put such Events into the back of slice and sorting them by size field.

func (s ByTime) Less(i, j int) bool {
    if s[i].timeEnd == nil || s[j].timeEnd == nil{
        return s[i].size < s[j].size
    }else {
        return s[i].timeEnd.(float64) < s[j].timeEnd.(float64)
    }
}

 a, b, c, d := Event{timeEnd:12.}, Event{timeEnd:nil, size:-10}, Event{timeEnd:56.}, Event{timeEnd:nil, size:2}
 queue := []*Event{}
 queue = append(queue, &a, &b, &c, &d) 

But as result I have:

[<nil> 12 56 <nil>] 

While expecting [12 56 <nil> <nil>] How to implement it correctly?

Here example in https://play.golang.org/p/FWU98npGtbU

Answer 1

In Less, you don't want to compare the sizes unless both timeEnds are nil and then you'd need to handle the "only one timeEnd is nil" cases separately. So you have four cases to consider not two:

func (s ByTime) Less(i, j int) bool {
    if s[i].timeEnd == nil && s[j].timeEnd == nil{
        return s[i].size < s[j].size
    } else if s[i].timeEnd == nil {
        return false
    } else if s[j].timeEnd == nil {
        return true
    } else {
        return s[i].timeEnd.(float64) < s[j].timeEnd.(float64)
    }
}