how many unique manufacturers are there in the following dataset? 

'The column Manufacturer is Apple., The column Model Name is MacBook Pro., The column Category is Ultrabook., The column Screen Size is 13.3"., The column Screen is IPS Panel Retina Display 2560x1600., The column CPU is Intel Core i5 2.3GHz., The column RAM is 8GB., The column  Storage is 128GB SSD., The column GPU is Intel Iris Plus Graphics 640., The column Operating System is macOS., The column Operating System Version is nan., The column Weight is 1.37kg., The column mfg_date is 2013-09-28., The column Price is 1429.5028176.The column Manufacturer is Apple., The column Model Name is Macbook Air., The column Category is Ultrabook., The column Screen Size is 13.3"., The column Screen is 1440x900., The column CPU is Intel Core i5 1.8GHz., The column RAM is 8GB., The column  Storage is 128GB NAME_1., The column GPU is Intel HD Graphics 6000., The column Operating System is macOS., The column Operating System Version is nan., The column Weight is 1.34kg., The column mfg_date is 2016-10-16., The column Price is 959.2049376.The column Manufacturer is HP., The column Model Name is 250 G6., The column Category is Notebook., The column Screen Size is 15.6"., The column Screen is Full HD 1920x1080., The column CPU is Intel Core i5 7200U 2.5GHz., The column RAM is 8GB., The column  Storage is 256GB SSD., The column GPU is Intel HD Graphics 620., The column Operating System is No OS., The column Operating System Version is nan., The column Weight is 1.86kg., The column mfg_date is 2013-05-06., The column Price is 613.548.The column Manufacturer is Apple., The column Model Name is MacBook Pro., The column Category is Ultrabook., The column Screen Size is 15.4"., The column Screen is IPS Panel Retina Display 2880x1800., The column CPU is Intel Core i7 2.7GHz., The column RAM is 16GB., The column  Storage is 512GB SSD., The column GPU is AMD Radeon Pro 455., The column Operating System is macOS., The column Operating System Version is nan., The column Weight is 1.83kg., The column mfg_date is 2008-12-16., The column Price is 2707.560648.The column Manufacturer is Apple., The column Model Name is MacBook Pro., The column Category is Ultrabook., The column Screen Size is 13.3"., The column Screen is IPS Panel Retina Display 2560x1600., The column CPU is Intel Core i5 3.1GHz., The column RAM is 8GB., The column  Storage is 256GB SSD., The column GPU is Intel Iris Plus Graphics 650., The column Operating System is macOS., The column Operating System Version The response should be in all capital letters.
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