Question

Doing a vertical reflection symmetry on dots on a screen, please consider the following.

scrWidthCM=40

originals={{14.2065, 10.609, 0.974938}, {19.5653, 6.92721, 0.974938}, 
           {30.4607,17.4802, 0.974938}, {27.4621, 10.0393, 0.974938}, 
           {15.915, 20.4278,0.974938}, {28.6921, 5.2132, 1.53205}, 
           {27.0317, 24.8346,1.53205}, {20.8853, 18.8588, 1.53205}}

Where each sublist corresponds to : {Xcoordinate,Ycoordinate,radius}

Applying the symmetrical transfer to each of the 8 points :

(scrWidthCM - #[[1]]) & /@originals

How could I replace the first value of each sublists rather than simply compute its reflected X coordinate ?

Answer 1

Assuming that you want to directly modify your originals object:

originals[[All, 1]] = scrWidthCM - originals[[All, 1]]

If you want a copy, then use:

{scrWidthCM - #, ##2} & @@@ originals