NC_CreateSampleReduction creates a file with all channels with mor than 2 million data points in the source file.
ret is smaller than 0 if an error occurred and otherwise greater than 0.
The function creates a new file with the suffix -red.nc2. The file will only be created if the source file contains channels with more than 2 million data points. The reduction factor is 1000. Example: A data file with the name input.nc2 contains 10 Channels with 2.5 million data points. The function creates a file with the name input-red.nc2 with 10 channels with 2500 data points.