Hi Yuri,
Tatiana has most of this right but I think that "I noticed it was a waste shopping." would be better expressed as .. "I thought that was a waste."

usually we talk about things being "a waste of time", rather than in another context, that's why "a waste of shopping" doesnt really sound natural.

example. "Well, buying that cat toy was a total waste of time."

Cheers,
Andrew.

Our cat.

We have a cat named Mii.
This is the cat that one of my daughters bought as she felt lonely when she had lived by herself.
She came back to our home last summer and brought the cat with her.
Since she doesn't feel lonely anymore, sometimes she forgets her cat so I have to take care of it.
When I start studying English, Mii comes and looks into my eyes and requests me to play with her.
Then I have to give up studying and I play with her using a ball, a string and foxtail grass.
I bought her a radio-controlled model car the other day, but she was scared of that. I noticed it was a waste shopping.