#Grouping eating measures(within gender)
girls_data$m_eating_behaviors=rowMeans(girls_data[,c("m_eating8", "m_eating7","m_eating4", "m_eating3"),], na.rm = TRUE)
Error in h(simpleError(msg, call)) :
error in evaluating the argument 'x' in selecting a method for function 'rowMeans': undefined columns selected