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Hi, Could someone help with coding this in R? I need to select one row per patient i in clinic j. The data is organized similar to that shown below. Two columns - patient i in column j identify each unique patient. There are two columns on outcome. Some patients have multiple rows with each row representing one visit, coded for in the column, visit. Some patients have just one row indicating

Hi, I was hoping someone could help figure out how to write code for R to do the below. I have data that looks like below. Variables, sid and pid are strings, slope is numeric. I need R to get me the mean of slopes for all pid's nested within each sid if there are more than one pid's nested within sid. If there is only pid for a sid, like for 2.1 below, I want R to write a 0. In the