[R] I have a question about a programa in R

[Sandra Esperanza Melo Martinez]

I am writing because I have a question with a program in R. I have some longitudinal data with repeated measures in different times, the individuals are infants who are measured the weight when they are born and through the time, but I have different time and different  number of measures with each infant because the mothers does not were to all the controls in the hospital, and I need to adjust a multilevel model but I have problems with the program in R.
 
Thank you so much for your answers to my question
 
I attach my file in R and the txt file.


      
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