private static Tensor reduceIndexedVector(IndexedTensor argument, Aggregator aggregator) {
        ValueAggregator valueAggregator = ValueAggregator.ofType(aggregator);
        int dimensionSize = Convert.safe2Int(argument.dimensionSizes().size(0));
        for (int i = 0; i < dimensionSize ; i++)
            valueAggregator.aggregate(argument.get(i));
        return Tensor.Builder.of(TensorType.empty).cell(valueAggregator.aggregatedValue()).build();
    }
Creates a reduce function.

@param argument the tensor to reduce
@param aggregator the aggregator function to use
@param dimensions the list of dimensions to remove. If an empty list is given, all dimensions are reduced,
                  producing a dimensionless tensor (a scalar).
@throws IllegalArgumentException if any of the tensor dimensions are not present in the input tensor
vespajlib/src/main/java/com/yahoo/tensor/functions/Reduce.java