R: mapply函数返回误差:各因子水平集不同

I have two dataframes (DfA and DfB). Each dataframe has three factor variables: species, type and region. DfA also has a numeric value column, and I want to use it to estimate numeric values in a new column of DfB, based on shared attributes.I have two dataframes (DfA and DfB). Each dataf