In the following data of item prices per store per year:
store iterm price time
0 cosco A 0.410847 2023
1 cosco A 0.429190 2022
2 cosco A 0.328295 2021
3 cosco B 0.462785 2023
4 cosco B 0.246153 2022
5 cosco B 0.871776 2021
6 target A 0.973494 2023
7 target A 0.447499 2022
8 target A 0.271210 2021
9 target B 0.065916 2023
10 target B 0.991374 2022
there are items from different stores with random prices for a selection of different times.
How can I find out price change (per year) considering that not all items are reported per all time? So in here result will look something like this: (numbers are random)
