Hi all, newbie in blender here.
I have a scene that is imported from structure synth consisting of 10000 cubes. I want to select all these cubes and replace them with the cylinder primitive. I only need to retain xyz of the objects. Seems easy but couldn’t get my head around it. Any help will be appreciated.
Thanks
Add a cylinder, select all the cubes and the cylinder (make sure the cylinder is the last object selected), Use Ctrl+L and select object data (blender 2.5x) or mesh data (blender 2.4x)
You may want to then make them single user U / 2 in object mode
Hmm thank you. IT doesn’t seem to work for some reason. Might that be because the import script is probably not creating the cubes as primitive meshes? When I do that, all the cubes disappear and I get one more cylinder.
If I try to create a cube inside blender and try the method, it works but not with the cubes that I’ve imported.
http://www.screencast.com/users/blenderwho/folders/Jing/media/2addc6b8-faa9-4fb5-96de-e839cb9ccf82
Being a primitive doesn’t matter, it is just making all the selected objects have the same mesh as the last object selected (the active object)
Maybe because all your cubes are one object?
If as Eris says your cubes are really one object, select it and in edit mode select all vertices (A) and press P to separate, selecting ‘by loose parts’
Thanks, I’ve been using the A key to select all objects so it never occured to me that they weren’t separate objects. 
CPU trying to separate all cubes in background as I speak. I’m pretty sure this will solve it.
Great community blender has! Thanks a lot.
One last question:
It took some hours for the computer to separate objects. Now I have all the cubes separated but their cursor (or what is it called? The thing with x y z arrows) is not where it should be. They are all parked at the same spot outside the scene. So when I Ctrl + L the new cylinders appear at the same point in the scene irrelevant to the cube’s actual position.
How can I make it so that cubes have their arrows at the right place?
After you have separated the cubes, select them all then:
In blender 2.54beta use Ctrl+Alt+Shift+C and select ‘Origin to Geometry’
In blender 2.49 go to Editing (F9) / Mesh panel, select ‘Center New’ button
Then you can link the cylinder mesh to them all.
Thanks again. Now all is fine.