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This transformation will perform a simple merge operation that functions as a data hierarchy. The picture below shows the functionality of a merge operation. First the most important time series is evaluated, if a value exists at a time in this series then this value will be used. If this is not the case, the second time series (series 2 in the example), will be evaluated. This procedure will continue until a valid value is found in one of the time series or until all time series are evaluated. If no valid value exists at time x in all of the input time series then a missing value will be returned unless the user has specified a default value with the fillGapConstant option. 
The hierarchy of the input will be determined by the order in which in input time series are listed in the
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