Hi,
I have set of points with attribute table (let just say with column "A"
containing 1s and 2s).
I would love to use function v.hull in order to get two convex hulls (their
faces). Basically apply function "by group". Unfortunatelly, I was not able
to find simple way to do that.

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First solution I came up with was scripting with for cycle using "category"
- picking ids of points and then run:
v.hull input=mypoints output=myhulls1 cat="1,3,40,etc"
v.hull input=mypoints output=myhulls2 cat="2,4,41,etc"
Than I tried where clause:
v.hull input=mypoints output=myhulls1 where="A<2"
v.hull input=mypoints output=myhulls2 where="A>1"
Unfortunatelly, this clumsy solution (I have hounderds thousands of point
sets) does not work. All four lines gave me the same result (convex hull
created from all points).
The only even more clumsy solution I succeded with was first use 'v.extract'
and than apply 'v.hull' on newly created maps.
My questions:
Is there a way how to effectively apply function(command) by group?
Is the v.hull function supposed to work like this (ingnoring where and cat
arguments)?
Thank you
Vil

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