I am currently working with a longitudinal dataset that consists of multiple waves. The variables in my dataset are named using a pattern like "A1STO," "A2STO," "B1STO," "B2STO," and so on. I want to keep only the variables from wave 4 onwards (i.e., "A4STO",...,"A10STO," "A11STO," etc.) and remove the variables associated with waves before wave 4.
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