How to count groups for a sequence SQL

Look on the following Oracle article - how to create groups for sequence records using SQL window functions :

select val

,row_number() over (order by val) as rn

,val-row_number() over (order by val) as grp

from

(values (1,2,3),(2,2,3),(4,2,3),(9,2,3),(10,2,3),(15,2,3)) t1 (val,a,b)

order by val

and the result:

|val |rn |grp |

|-----------|-----------------|------------------|

|1 |1 |0 |

|2 |2 |0 |

|4 |3 |1 |

|9 |4 |5 |

|10 |5 |5 |

|15 |6 |9 |

source: https://community.oracle.com/docs/DOC-915680