1. It's a kind of shopping by computer.

2. It's a kind of shopping on the computer.
3. It's a kind of shopping on-line.
4. It's a kind of on-line shopping?
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Are they all the same? Can we use 'on the computer' instead of 'by computer'?

2 answers

What exactly is this for, my dear? I would say that 3 & 4 are the same for sure. Don't use number 1, unless you have to. I really don't think that number 1 makes sense. 2 is ok, but again, use 3 & 4. Those make the most sense. Hope this helps!
All four are correct.

The phrase "on the computer" is more common, but "by computer" is not incorrect.