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Extracting information from lists


Does anyone know of a function that will allow me to extract the positions 
of the first elements of runs of similar elements within a list. For 
example, suppose that

list={7,9,1,6,8,1,1,6,5,1,1,1,8,7,6,1,1,1,1,7}

I need a function that will return

{3,6,10,16}

corresponding to the runs {1},{1,1},{1,1,1},{1,1,1,1} within list

Many thanks

Tony 


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