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[Jan Stránský <question691285@xxxxxxxxxxxxxxxxxxxxx>]

Question #691285 on Yade changed:
https://answers.launchpad.net/yade/+question/691285

Jan Stránský proposed the following answer:
Hello,

thanks for the code, but next time please try to create a MWE, where M stands for "minimal" - a few facets, no external mesh, just a few balls, no VTKRecoder... (sometimes, but very seldom, the full original code is needed).
Just focusing on your problem, which is saving same specific data.

> to extract and save at each time step

of course it is possible, but I would consider a longer period

> i need to save in the Txt format, which can be used with other
softwares.

please be more specific what "Txt format" and "other softwares" are.
**I personally** prefer to save data in some "structured" format like JSON or YAML. Creating "plain text" from them is easy, the other way not.

I think the plot module is not suitable for this kind of exporting. I
would save it "manually", see below.

### not tested, I am only willing to test it on a MWE :-)
import json
...
def exportForces():
   data = [] # list of data for each interaction
   for i in O.interactions:
      b1,b2 = [O.bodies[i] for i in (i.id1,i.id2)]
      # skip interactions not containing facets
      if not (isinstance(b1.shape,Facet) or isinstance(b2.shape,Facet)):
         continue
      # gather desired values
      fn = i.phys.normalForce
      fs = i.phys.
      cp = i.geom.contactPoint
      pd = i.geom.penetrationDepth
      # add it to the data collection
      d = dict(normalForce=fn,shearForce=fs,contactPoint=cp,penetrationDepth=pd,id1=i.id1,id2=i.id2)
     data.push(d)
   # save
   fName = "data{:06d}.json".format(O.iter)
   with open(fName,"w") as f:
      json.dump(data,f,indent=2)
...
O.engines = [
   ...
   PyRunner(iterPeriod=1,command="exportForces()"),
]
...
###

cheers
Jan

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