I have a vector shapefile of river networks, where each reach in the networks has its own row in the attribute table. I want to add a grouping column to the attribute table indicating which network the reach belongs to, e.g.:

a two network example:

and my attribute table:

I would like an additional column in the attribute table called "network" which would be filled with 1, 2, ....n indicating which network the given reach belongs to (in the example above "network" would be 1 or 2 since there are only two networks), it doesn't matter which network is 1 and which is 2.

I imagine this is trivial, I'm just learning, any help much appreciated.

I have a vector shapefile of river networks, where each reach in the networks has its own row in the attribute table. I want to add a grouping column to the attribute table indicating which network the reach belongs to, e.g.:

a two network example:

and my attribute table:

I would like an additional column in the attribute table called "network" which would be filled with 1, 2, ....n indicating which network the given reach belongs to (in the example above "network" would be 1 or 2 since there are only two networks), it doesn't matter which network is 1 and which is 2.