Huangzj
51 lines
1.7 KiB
Go
51 lines
1.7 KiB
Go
package linq
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// GroupJoin correlates the elements of two collections based on key equality,
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// and groups the results.
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//
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// This method produces hierarchical results, which means that elements from outer query
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// are paired with collections of matching elements from inner. GroupJoin enables you
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// to base your results on a whole set of matches for each element of outer query.
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//
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// The resultSelector function is called only one time for each outer element
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// together with a collection of all the inner elements that match the outer element.
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// This differs from the Join method, in which the result selector function is invoked
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// on pairs that contain one element from outer and one element from inner.
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//
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// GroupJoin preserves the order of the elements of outer, and for each element of outer,
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// the order of the matching elements from inner.
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func (q Query) GroupJoin(
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inner Query,
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outerKeySelector func(interface{}) interface{},
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innerKeySelector func(interface{}) interface{},
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resultSelector func(outer interface{}, inners []interface{}) interface{},
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) Query {
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return Query{
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Iterate: func() Iterator {
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outernext := q.Iterate()
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innernext := inner.Iterate()
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innerLookup := make(map[interface{}][]interface{})
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for innerItem, ok := innernext(); ok; innerItem, ok = innernext() {
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innerKey := innerKeySelector(innerItem)
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innerLookup[innerKey] = append(innerLookup[innerKey], innerItem)
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}
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return func() (item interface{}, ok bool) {
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if item, ok = outernext(); !ok {
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return
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}
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if group, has := innerLookup[outerKeySelector(item)]; !has {
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item = resultSelector(item, []interface{}{})
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} else {
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item = resultSelector(item, group)
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}
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return
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}
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},
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}
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}
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