Hi @samber,

Unfortunately, SliceToMap (actually Associate which implements SliceToMap), as well as FilterSliceToMap, doesn't pass index of original collection item to transform func:

func Associate[T any, K comparable, V any](collection []T, transform func(item T) (K, V)) map[K]V {
	result := make(map[K]V, len(collection))

	for i := range collection {
		k, v := transform(collection[i])
		result[k] = v
	}

	return result
}

It makes SliceToMap insufficient (ineffective) in some cases, like the one which @renom described and which can be implemented only with additional temporary collection (https://go.dev/play/p/QH80tW3tM5K):

list := []string{"string 1", "string 2", "string 3"}
result := lo.FromEntries(lo.Map(list, func(str string, index int) lo.Entry[int, string] {
	return lo.Entry[int, string]{
		Key:   index,
		Value: str,
	}
}))

IMHO, for all functions which take slice as an input (source) collection, we need to pass item index into transformation function (but it's too late to make such backward incompatible change, so we may need to consider introduction of new functions for slice → map conversions). In case of SliceToMap the new function could look like (https://go.dev/play/p/n1ehTa4lyjN):

func SliceWithIndexToMap[T any, K comparable, V any](collection []T, transform func(item T, index int) (K, V)) map[K]V {
	result := make(map[K]V, len(collection))

	for index, item := range collection {
		k, v := transform(item, index)
		result[k] = v
	}

	return result
}

Thank you.

Uh oh!

Converting slice to map (new helper) #601

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