Return observations with available values. The operation skips over all keys with missing values (such as values created from `null`, `Double.NaN`, or those that are missing due to outer join etc.). [category:Accessing series data and lookup]

Create a new series that contains values for all provided keys. Uses exact lookup semantics for key lookup - use `lookupAll` for more options ## Parameters - `keys` - A sequence of keys that will form the keys of the retunred sequence [category:Accessing series data and lookup]