Check that input variables to melt are appropriate.
melt_check(data, id.vars, measure.vars)
list id variable names
list of measured variable names
Hadley Wickham <h.wickham@gmail.com>
data frame
Vector of identifying variable names or indexes
Vector of Measured variable names or indexes
If id.vars or measure.vars are missing, melt_check will do its
best to impute them.If you only
supply one of id.vars and measure.vars, melt will assume the remainder of
the variables in the data set belong to the other. If you supply neither,
melt will assume character and factor variables are id variables,
and all other are measured.