acess previous point attribute in wrangle

[vijayakumar]

Hi guys,

need help in vex. I tried creating an attribute in for loop and access the previous point value . But i couldn't access the created value. Here is the code. in this i am creating an integer a and storing the value. i am trying to use point(geoself) and access the previous point attribute but it defaults to zero. help me out with this.. thanks..

 

int @a=1;
int @test[];
int @inst;
if(@ptnum==0)
@test[0]=1;
for(int i=0;i<=@ptnum;i++)
{
@a=@a+i;
if(@ptnum>0)
{
@inst=point(geoself(),'a',i-1);   //cannot access the previous value
@test=point(geoself(),'a',i-1);

}

}

[f1480187]

You need to do such things in different wrangles, because geometry wrangles are writing attribute values at the very end of execution.

// First Point wrangle.
i@a = (@ptnum+1) * @ptnum / 2;

// Second Point wrangle.
i@a_prev = point(0, "a", @ptnum-1);

 

Or use Detail wrangle, use explicit functions for setting attributes and keep track of previous values manually:

// Detail wrangle.
int a = 0;
int a_prev = 0;

addpointattrib(0, "a", a);
addpointattrib(0, "a_prev", a_prev);

for (int i = 0; i < @numpt; i++)
{
    a_prev = a;
    a = (i+1) * i / 2;

    setpointattrib(0, "a", i, a);
    setpointattrib(0, "a_prev", i, a_prev);
}

The drawback of using Detail wrangle is that you need to use explicit functions, which is a bit more lines of code. It is also single-threaded, but still very fast in most cases.

 

previous_point_value.hipnc

Edited August 26, 2016 by f1480187

[vijayakumar]

Thanks a lot