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I have a requirement to perform a series of GeometricTransformation[]s using the AfineTransform[] function. I use these to set up something similar to a kinematic chain in something similar to a mechanism.

Four geometric objects are stored in a list, say

fList={f1, f2, f3, f4}

and four affine transforms are stored in their own list, say

tList={t1, t2, t3, t4}

Right now I am performing the geometric transformations as follows

f1New=Fold[GeometricTransformation[#1,#2]&, fList[[1]], tList[[1;;1;;-1]]];
f2New=Fold[GeometricTransformation[#1,#2]&, fList[[2]], tList[[2;;1;;-1]]];
f3New=Fold[GeometricTransformation[#1,#2]&, fList[[3]], tList[[3;;1;;-1]]];
f4New=Fold[GeometricTransformation[#1,#2]&, fList[[4]], tList[[4;;1;;-1]]];

However, I would like to combine the four lines into a single line that generates a list of four new transforms and write a function to apply the transforms for lists of N graphics objects and N affine transforms.

So far I have tried to use Nest[] but that has not worked. I'm sure there is a subtle way to handle this but it eludes me. I would appreciate a hint.

Also, I am trying to stay away from using For[] or Do[] constructs because I am fascinated by Mathematica outstanding proficiency at handling lists.

Thank you and all the best!

B

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If elements of tList are TransformationFunctions, you can use a combination of Composition and MapThread:

cList = Composition @@ Take[tList, #] & /@ Range[4];

fListNew = MapThread[GeometricTransformation] @ {fList, cList};

to get the same result.

Example:

fList = {f1, f2, f3, f4} = {Point[{2, 4}], Rectangle[{4, 3}, {5, 5}], 
   Circle[{4, 1}], Polygon[{{1, 2}, {3, 3}, {2, 1}}]};

tList = {t1, t2, t3, t4} = {ReflectionTransform[{-1, 1}], 
   ShearingTransform[Pi/4, {1, 0}, {0, 1}], 
   TranslationTransform[{2, 3}], 
   ScalingTransform[{.5, 2.}]};

 f1234New = Fold[GeometricTransformation[#1, #2] &, fList[[#]], 
     tList[[# ;; 1 ;; -1]]] & /@ Range[4];

 fListNew = MapThread[GeometricTransformation] @ 
    {fList, Composition @@ Take[tList, #] & /@ Range[4]};

Row[Framed[Graphics[{PointSize@Large, FaceForm[Opacity[.5, Red]], 
      EdgeForm[Gray], Thick, #}, ImageSize -> 200]] & /@ 
  {fList, f1234New, fListNew}, Spacer[50]]

enter image description here

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  • $\begingroup$ Thank you @kglr The MapThread[] and Composition[] combo works well and it's very elegant, if I may say so myself. I assume that in your example you have meant fList={f1, f2, f3, f4} = ... and tList={t1, t2, t3, t4} = ... $\endgroup$ – user74549 Oct 12 '20 at 5:15
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    $\begingroup$ Thank you @user74549; fixed the definitions. $\endgroup$ – kglr Oct 12 '20 at 5:23

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